Windows XP Powertoys are capabilities created by Microsoft that were supposed to be included when XP was released, but for whatever reason were not. As a result, they made these features available as Powertoys that integrate with the operating system. For example, if you wanted to mimic the multiple Desktops feature of Linux distributions or be able to see a screenshot of whatever applications are running when you press Alt + Tab, the Powertoys provide the ability to do that. You can download them from Microsoft and give them a try. I personally use the Virtual Desktop Manager, Tweak UI, Alt-Tab Replacement, and ClearType Tuner on my machines.