Here's an easy way to delete your prefetch -- Automatically!!
1. Go into My Computer and go into your hard drive.
2. Right-click anywhere that a file is not and select the 'New' submenu and click 'Text Document'
3. Name it "deleteprefetch"
4. Double-click on the text file you just created.
5. Type "del C:\Windows\Prefetch\*.* /Q" (without the quotes).
6. Go to File > Save As... and choose "All Files" from the "Save as Type" box and save it as "deleteprefetch.bat"
7. You just created a batch file that will automatically delete all the files in your Prefetch folder. Congrats.