Prefetch is one of XP's best speedup systems it keeps program startup information available to XP so that it can find and run the program faster. Unfortunently, it will do this for all apps that are started up, even ones that only run once and then are deleted.

so, it is a good idea to delete the contents of the prefetch folder once in a while, or even on a weekly basis using Scheduled Tasks.

open up the Command Prompt box. Type in the following;

Echo off
del c:\windows\prefetch\*.* /q

Save this batch file in Documents or where ever as 'Clean Prefetch.bat'. Then make a shortcut to it, and put the shortcut somewhere so that you can find it and even set up Scheduled Tasks so that it may run whenever.
now, when your apps startup a little too slow, clean out the prefetch.

To modify how prefetch operates, go to the registry line;

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters

on the right pane, there will be a key 'EnablePrefetcher' with a number..

* 0—Disable
* 1—Application Launch Prefetch
* 2—Boot Prefetch
* 3—Prefetch everything

3 is the obvious best.
Finally, here is a neat startup trick and I mean an app startup trick, not just a system startup trick.
On any app that you startup, even the ones in the Startup folder (it is best to use StartUp.cpl for this) for the ones at startup.
and StartUp CPL has just been upgraded to version 3.0 from 2.8 still called 2.8, but fixed some bugs.
right click over the shortcut to that app click the shortcut tab, and then in the target section, where you see something like the following (I am useing FireFox for this example)

"F:\Program Files\Mozilla Firefox\firefox.exe" /Prefetch:1
add, as in the above example, add in the /Prefetch:1
this will give that app the first startup priority, every time.

as a final note, this tweak will not always work for every app, so test each one individually also, any apps in the StartUp folder in the All Programs section from the Start Button menu, should be edited at the shortcuts in that folder does not seem to work from the Startp CPL app, but the other sections do.