One way to ease Windows users into GNU/Linux is to encourage them to try free software that runs on both operating systems. Many people are already using Firefox and OpenOffice.org on Windows, but a host of other applications are also cross-platform, including the GIMP and Inkscape. Using these applications is the best way I know of to ease fears that free software is in any way inferior to proprietary. Moreover, when Windows users do try GNU/Linux, they'll feel more at home because they're already familiar with the applications.
You can expand this effort by installing KDE on Windows, which allows you to run applications designed for the KDE desktop in Windows. Although still under heavy development, this is another way to make Windows users comfortable with free software (another project, KDE on Mac OS X, is bringing KDE to that operating system as well).
Yet sooner or later, exploring GNU/Linux from Windows comes down to one of five main options:
Using some form of emulation or virtualization.
Creating a Live CD.
Creating a Live USB drive.
Running GNU/Linux from the same partition as Windows.
Dual-booting is by far the oldest way of encouraging Windows users to try GNU/Linux. During installation of GNU/Linux, you create separate partitions for the operating systems, and add a boot manager to the system. Then, when the computer starts, you choose which operating system you want to use.
Dual-booting is ideal for Windows users who still need a particular application. Its main drawback is that, even though GNU/Linux installation programs are now easy to use, many of the steps involved -- particularly partitioning drives and adding a boot manager -- sound scary to the average Windows user. You may need to persuade your Windows-using friends that the process is safe, and you should probably be prepared to guide them through the process.
Another consideration is the size of the available hard drive. Although this is less a problem than it was once, people with large music or movie collections may still be hard-up for space and not feel like adding another hard drive so they can experiment. A possible solution may be to use Gparted to create a partition for personal files that can be shared by both operating systems. That way, you only need about a 30 gigabyte partition for Windows, and a 15 gigabyte one for GNU/Linux.
But the greatest drawback to dual-booting is that its only suitable for those who have a serious interest in GNU/Linux. By the time you download an installation disk, do the installation, and customize the desktop, three or four hours have probably elapsed. What's more, undoing the dual-boot is likely to take another hour or more. For this reason alone, dual-booting is not an option for those who are only casually curious. It's more a way to wean someone off Windows who is already determined to break lose.
Emulation and virtualization
Emulation and virtualization are techniques for running one operating system within another.
Using proprietary software such as VMware or free software such as VirtualBox, you can run multiple versions of GNU/Linux from within Windows. However, setting up these options may be more than curious Windows users want to face. Also, having at least a gigabyte of RAM for each operating system involved is necessary if you want decent performance.
The main shortcoming of these distributions is that they integrate into the Windows desktop, rather than presenting a GNU/Linux one. They do not, for instance, give users the opportunity to use multiple workspaces, or to try desktop customization options. But, since each installs, runs, and uninstalls as though it were another Windows program, most people should have little trouble using it.
A live CD or DVD is one that you can use to start your computer. Live CDs became popular in GNU/Linux in 2003 with the release of Knoppix, although they existed before then.
Today, almost every distribution includes Live CD versions on their download pages, especially user-friendly ones like Ubuntu or Fedora. To use one, you must download the CD or DVD image file (both of which have an .iso extension), then create a disk from the file. Your burning software will have an option for working with an image file that is separate from the one for creating a data disk.
When you have burned the disk, place it in the drive and re-start your computer. As your computer boots, you may need to change its boot order from the hard drive to the CD/DVD drive. Depending on your machine, you may have to press a key or sequence of keys to change the boot order, so that it boots from the CD/DVD drive instead of the hard disk. This change is made either in a separate menu or in the BIOS. If you watch as your computer starts, you will see a message telling you what keys you need to press.
Most Live CDs will boot to a GNU/Linux desktop. Some, however, stop at the login screen and require that you enter a user name and password before you reach the desktop. You can find the user name and password you need on the download page from which you got the image file.
The main advantage of a live CD is that you can boot into GNU/Linux without making any changes to your system. While you can access your hard drive from a live disk, you have to make a deliberate effort to do so, and most basic users will have no idea how to make that effort.
A live CD is also useful as a recovery disk. If you want secure computing, or the ability to carry a familiar operating system for use in whatever computer you happen across, you can use a live CD with a flashdrive on which to save your files.
The disadvantage of live disks is that they are slow compared to a hard drive. Used on a laptop, which is generally slower than a workstation, they can be painfully slow. The first time you start a computer with one, you may wonder if it's stalled, and on the desktop programs will start slowly. The impression that new users might get is that GNU/Linux is much slower than Windows, when usually the opposite is true.
You cannot do much about this lack of speed. However, you can minimize it if you choose a distribution designed for older computers, such as Damn Small Linux, or one optimized for speed, such as many of the Slackware-based distributions, such as NimbleX.
Live USB drives
Live USB drives are similar to a Live CD/DVD. Typically, though, Live USB drives are not on the download pages of your distribution of choice. Instead, they are usually developed by a sub-project that you can find by a quick Web search.
Live USB drives have all the advantages of a Live CD, and none of the disadvantages. Although slower than a hard drive, Live USB drives are much faster than a Live CD, and can hold much more information. Many, too are persistent -- that is, you can store files and make permanent changes to the desktop, neither of which you can do from a Live CD. All of which means that a test drive using a Live USB is far closer to the experience of using GNU/Linux on a workstation.
However, in many cases, you need a machine with GNU/Linux installed to create the Live USB drive. A notable exception is Fedora's LiveUSB-Creator, a script that runs a wizard in Windows XP or Vista to step you through the creation of the live flashdrive.
Another consideration with a Live USB drive is that you need at least a 2 gigabyte flashdrive if you want a persistent test drive. While a CD or DVD is only a couple of dollars, you might think twice about spending $40 to let someone experience GNU/Linux on a flash drive.
Sharing a drive with Windows
The most recent choice for exploring GNU/Linux from Windows is Wubi. The program is designed to install Ubuntu -- its name is short for "Windows Ubuntu Installer" -- but similar tools for other applications are likely to appear soon.
Wubi installs a version of Ubuntu to the partition on which you have installed Windows, and adds a bootloader to give you the option to run Windows or Ubuntu when you start the machine. When I reviewed Wubi back in April, the installer assumed that users would have reasonably advanced computer knowledge, but the performance of Ubuntu was slowed only by the fact that Windows file systems tend to be slower than GNU/Linux ones. It also uninstalled cleanly when I was finished, leaving very little to ask for.
Choosing a method
Each of these test drive methods has pros and cons. Which you choose depends on the effort you want to spend in introducing GNU/Linux, what you want to highlight, and the interest shown by your audience.
For those who want a minimum of fuss, a Live CD is hard to beat. It does not affect what is already on the machine, and is a cheap way to satisfy curiosity quickly. If the slow speed of a Live CD bothers you, then a Live USB drive will give you a better sense of GNU/Linux's performance, but at a higher cost if you don't happen to have a spare flashdrive handy. Performance is better indicated by emulation or virtualization, but setting up any of those choices requires more time and effort than curiosity might warrant.
The best all-round method for test driving is probably Wubi, because its straightforward and offers good performance without requiring any extraordinary resources on the test machine. Some Windows users, though, might be made uneasy by its use of a boot drive, and lay users might find the installer assumes knowledge that they lack.
However, for those who are more than idly curious, dual booting remains the best choice for test-driving, especially when you set up a data partition that both operating systems can use. On a dual-boot system, you can see the full power of GNU/Linux, but still use Windows if you feel the necessity. The only reason you might hesitate is if you lack hard drive space.
The best choice, of course, is probably to install GNU/Linux on a spare machine, which is even easier than dual-booting and removes any fears about loss of data. However, if the Windows users around aren't ready for that effort or commitment, any of these methods can be a reasonable alternative, depending on the circumstances.