Modding the GUI
We can begin the metamorphis with a couple of quick downloads:
Desktop Wallpaper
In the process of transforming Windows XP into a Mac OS X lookalike the easiest change we can make is to the desktop wallpaper. (use "Display Properties" in the "Control Panel" to change your desktop wallpaper)
Windows Media Player - iTunes
Many of today's modern applications support the use of "skins" to customise their cosmetics and, sometimes, their operation. Microsoft's Windows Media Player 9 is no exception. Want your WMP to look like OS X's "itunes"? An "iTunes" skin for WMP is available (preview). When the download is complete you will need to unzip the skin before you can install it.
Mozilla
Mozilla is a web-browser (like Microsoft's "Internet Explorer", only much, much better). The browser can be completely customised with skins, as can its associated applications. The very best skin we have found is "aquaMoz", which maintains the look and feel of the OS X environment (preview).
UPDATE (14th May, 2004): I have also managed to recreate Safari with a Firefox mod, which I covered over in the Weblog.
Screensaver
We can change our screensaver to one with an OS X "feel". This screensaver bounces a simple, graphite Apple logo around the screen (over a white background). It supports multiple monitors.