Prefetch is a new feature in Windows XP in which the Operating System will fetch required info and store it in a specific location...then when XP boots up it can load everything up significantly quicker by just running the commands in this folder.

However, after installing new programs, removing old ones, and everything else that happens on your pc, your prefetch ends up getting clogged up with a bunch of links and references that are no longer valid, in effect slowing down your pc.

It's a good idea to clean it out once a month, to increase boot up time. The first time you boot up after clearing your prefetch will take longer than normal while Windows repopulates this folder, but after the first boot up you will notice increased boot-up speed.

To clear your prefetch, simply go into C:\Windows\Prefetch and delete everything in here.

Reboot and you are done.