If you want to add space to a drive, store personal data on a separate partition from your operating system, or run multiple operating systems from the same hard drive, then you need a partition editor.
Traditionally, this is a field where alternative operating systems have always lead in the available tools. PartitionMagic, the first partition editor, started life as an OS/2 program for users who wanted to dual boot, and GNU Parted brought partition editing to the GNU/Linux command line in 1999. Since then, various interfaces -- most notably, GParted -- have tried to bring GNU Parted's functionality to the desktop.
However, from what I've seen, by far the most successful of these efforts is the newly released PartedMagic version 3.0. The name suggests that PartedMagic is meant as a free alternative to proprietary tools like PartitionMagic -- a goal in which it easily succeeds, despite a mildly eccentric desktop.
PartedMagic consists not just of GParted, but also of a mini-distribution that includes tools you might need while re-partitioning a hard drive. Available in both a CD and USB flashdrive image, at 44.5 megabytes, PartedMagic is quick to download and burn. It is also noticeably quicker to run than the average live CD, which is a relief, given that a slow response time can easily cause you to make mistakes when you are resizing or moving multiple partitions.
Starting PartedMagic, you have the option of using the default Xorg graphics server, or, if that fails, Xvesa or the command line, from which you can use the plain but serviceable GNU Parted. As the graphical version loads into RAM, the CD ejects, relieving you of the need to worry about it later.
If you are new to editing partitions, then before you start, you should learn the difference between primary and extended partitions, noting especially why you can only have four primary partitions and must use an extended partition if you want more.
Similarly, if you are unfamiliar with how GNU/Linux names partitions, you need to know that your C: drive under Windows is probably labeled /dev/sda1 in PartedMagic, meaning it is on the first hard drive (a) and is the first partition (1). To avoid accidentally editing the wrong partition, you might want to use the label command in Windows to give each existing partition a unique name that you can read in PartedMagic.
If you choose a graphical server, PartedMagic boots directly on to an Xfce desktop that has unnecessary features such as wallpaper customization removed. For some reason, though, it still has four workspaces (that is, multiple desktops), a choice that eats up available memory and slightly slows performance.
The main desktop modification is that, instead of having the menu on the left of the panel, with other icons shifted to the left to be adjacent, PartedMagic puts its basic partitioning tools on the far right, with the main menu third from the right. These changes seem needless, but can be quickly detected. If you want, you can even move the main menu to its traditional place on the panel, then use the Saving Parted Magic script in the menu to back up your changes so you can re-use them in your next session.
There is also a system summary on the desktop, although it is of minimal use, since you are unlikely to care much about the kernel PartedMagic is running or the uptime of the live CD. Possibly, though, you just might care about the main processes that are running, in case you run short of space and need to kill one or two of them from the command line provided.
PartedMagic's basic tools are available on each side of the main menu icon. They include a terminal (useful for advanced users who know how to use the utilities for various partition formats, or for those wanting to make sure that all partitions are unmounted and ready for editing); a choice of PCMan or Midnight Commander for a file manager; and networking tools, ranging from XChat to Firefox (useful if you need more information on what youre doing or want to connect to the Internet for help, though a browser with a smaller footprint might be a better choice).