If you're like me your system only has about 128megs of RAM. The Windows XP Prefetch can take a lot of this up by preloading programs at boot as well as preloading programs you often use thus sucking away your available RAM.
On my system, a Dell PIII 866 with 128 megs of RAM, I was able to greatly boast my system performance by disabling Prefetch all together. It used to take a half hour for the disk to stop thrashing after stopping Nortons SpeeDisk, Now it stops instantly.
Note: This tweak worked for this user and their system configuration but disabling prefetch on other systems may have a bad effect as it might free up ram but it also could increase program start up time.
Here's how to disable Prefetch.
1. run "regedit";
2. goto [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnablePrefetcher];
3. Set the value to either 0-Disable.