To boost a computers performance running Windows XP, I suggest the following should be done:

1.Uninstall as many programs as you possibly can.
2.Make sure that you run as few programs simoultaneously as possible, check the startup entries in the registry and delete the unnecessary entries.
3.Use a maximum of 1/3 of the total disk space. If not enough disk space, then upgrade.
4.If you run much stuff in real-time, make sure you have so much RAM memory available that the computer seldomly needs to swap data.
5.Use NT file system, not FAT32.
6.Stop unnecassary windows services.
7.Defragment your drives on a regular basis.
8.Scan your computer for spyware on a regular basis.
9.Log on as a user with restricted access. (active directory consumes much)
10.Only install necessary programs.
11.Avoid running antivirus programs, firewalls etc.
12.Use a single color as wallpaper.
13.Inactivate active desktop.
14.Avoid running the computer in a network environment.
15.Use a hard drive and motherboard that supports native command queuing. SCSI or SATA.
16.Use a CPU with hyperthreading technology
17.Disable all available schedulars and automatic updates of all kinds.
18.Minimize all windows that are not used.
19.Select the combination of IDE devices and channels carefully.
20.Shut down the computer on a regular basis.
21.Disable IE caching.
22.Update the OS with service packs on a regular basis.
23.Update the drivers on all devices.