here. Microsoft PowerToys are tiny programs (most of them below 1MB in size) that adds great functionality to Windows XP. There are many PowerToys on the site, some are simple like the Webcam Timershot that allows you to snap pictures from your Webcam at regular intervals. The Power Calculator adds graphical calculator functions to the vanilla Windows Calculator. However, my favourites are the Alt-Tab Replacement and the Tweak UI.
The Alt-Tab Replacement simply adds previews of the application window you are switching to and the Tweak UI allows you to really fine tune XPs user interface (like taskbar settings, mouse settings etc) to suit your preferences.
Unmissable if you use XP. Link