The two things XP most detests are insufficient memory and full disks.
1GB RAM is a good place to start. 2GB is better. 3GB or 4GB (depending on DIMM configurations but you won't be able to use all 4GB) even better, but don't forget to put the /3 option into the boot.ini setup.
Any disk with less than 30% free space will cause you grief at some time. Get rid of all the accumulated crud. If you have downloaded installers, write them to CD/DVD and delete.
Install the SysInternals utilities. Run pagedfrg at every boot, at least until it says all the files it works on are each in 1 fragment.
Defrag the disk. You might have to do that several times with reboots in between for pagedfrg to finish its cleanup.
I don't regularly clear the prefetch. It should not need it more often than once after each set of windows patches. (OK. That's about once a day anyway.
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