KDE on Windows is such a subversive project that it is impossible to resist. Who else except the free and open source software (FOSS) community would take a desktop for Unix-like systems and port it to Windows, co-opting the very operating system that community members love to hate?
On second thought, however, the idea is not so quixotic as you might expect. Ports of FOSS desktop to Windows like Ubuntu's Wubi and the Ulteo Virtual Desktop already exist, and the Qt toolkit with which KDE is built already has a Windows version. Under these circumstances, a release of the current KDE 4.2 on Windows is less unimaginable than you might initially think.
True, the dependability and functionality fall short of what could be called a stable release. Still, version 0.9.5-0 of KDE on Windows is reliable enough to give a tantalizing glimpse of what it should soon become, as well as an unparalleled chance to compare FOSS and proprietary applications side by side. The only real question is what audience KDE on Windows is supposed to be aimed at.
The easiest way to install KDE on Windows is to download the installer and run it from your Windows desktop. Windows 2000, XP, and Vista are all supported. The installer is possibly complicated enough that it will make the average Windows user uneasy, but, since it results in a non-destructive installation thats easy to remove, nobody should be intimidated by it.
Mostly all you need to do is follow the instructions slowly and carefully, accepting the defaults wherever you don't understand. In this way, you can quickly move through the first part of the installer, choosing to install from the Internet, using C:Program Files as the installation directory, and choosing Enduser as the install mode.
Then you can navigate the mysteries of selecting a mirror by choosing the download site nearest to you, and choosing the latest stable version of KDE on Windows to install. At that point, you just need to select everything to install, and choose any additional language support you want besides the default American English. After that, installation is a matter of watching a progress bar for fifteen minutes.
When the installation completes, you can find KDE applications at Programs -> KDE 4.2.00 Release in the Windows Start Menu. Should you want to update the KDE applications, or add new ones as they become available, you can run the installer again.
You can also use the installer to remove KDE on Windows. Since all the files are in the same directory, the removal is trouble-free.
So far, KDE on Windows includes only a limited number of applications. Applications not specific to KDE, such as Firefox or the GIMP, are not installed -- although you can find Windows version of many of them. Other KDE applications, such as the KRunner application center or the Klipper clipboard, are still unavailable. However, what is installed is a well-rounded set of programs, including the latest beta of KOffice 2.0, the Gwenview image viewer, the Amarok media player, and the Konqueror web browser. Games and educational software are particularly well-represented.
The performance of most of applications is as quick as on GNU/Linux, but there are occasional lapses in performance. For example, some programs, like the Klines game, are slow to start. On my system, Amarok crashes, while the Kate text editor sometimes locks up briefly for no obvious reason. Nor can you make a FolderView your desktop, although the menu item to do so is available. No KDE on Windows program is able to use the Windows clipboard yet, and closing any program gives you a notification of a memory error, though you can close the message window and continue working without any consequences.
Another problem is that KDE programs cannot use Windows versions of Flash or Java, and KDE on Windows does not provide free versions of these programs such as Gnash or OpenJava -- perhaps because they are not native to KDE.
Such shortcomings aside, performance is more or less adequate. In general, applications run well enough that you can give KDE for Windows a thorough exploration, and even do a little work using them, so long as you remember the limitations.