I found this in a few different places around the 'net - hopefully it's helpful:
Clean Your Prefetch to Improve Performance
This is a unique technique for WinXP. We know that it is necessary to scrub registry and TEMP files for Win9X/ME/2000 periodically. Prefetch is a new and very useful technique in Windows XP. However, after using XP some time, the prefetch directory can get full of junk and obsolete links in the Prefetch catalog, which can slow down your computer noticeably.
- Open C(system drive):/windows/prefetch, delete those junk and obsolete files, reboot. It is recommended that you do this every month.