By default Windows XP indexes files on your hard drive and stores them in memory to speed up its’ built-in search. But if you rarely use Windows search, turn off indexing to free up memory and CPU horsepower for the files and applications you actually do use. A few simple how-to steps after the jump.

To turn off indexing:

Open up “My Computer.”
Right-click on your hard drive (usually “C:”) and choose “Properties.”
Uncheck the box at the bottom that reads “Allow Indexing Service to…”
Click OK, and files will be removed from memory. This removal may take a few minutes to complete.
To disable the indexing service:

In the “Start” menu, choose “Run.”
Type “services.msc” and press Enter.
Scroll-down to “Indexing Service” and double-click it.
If the service status is “Running”, then stop it by pressing the “Stop” button.
To make sure this service doesn’t run again, under “Startup Type:”, choose “Disabled.”
Windows search will still work if you perform these steps, but it will work more slowly than if indexing was enabled.
http://lifehacker.com/031440/turn-off-indexing-and-speed-up-windows-xp