You can't do much to reduce the size of XP. The OS needs close to 3 Gb to
live comfortably.
What you can do is run disk cleanup, and delete any temp files etc. Backup
any large files to CD and delete them from the disk i.e., pictures, music,
game memories etc.
Take a look at the installed programs, any that you don' use, uninstall
them.
You didn't say what size hard-drive you have. you might consider installing
a second one. They don't cost all that much these days.
LOL JAX