Lots of good advice, but lets start with the basics....
install Norton System Works(complete), install Spy Sweeper, install Window Washer, install Mail Washer PRO.
Do all of the updates and upgrades so everything is current.
Now run Window Washer
Then run Norton "find and fix" (Win Doctor)
then run Spy Sweeper,
Run Find and Fix again.
Now run Norton "Speed Disk"
then finally run Norton Anti Virus.

your machine will be clean, and ready to rock and roll. I have been running this software for 4 years on the same laptop with XP Home (SP2) and have never had a problem.

You might look into another ram chip... drop in a 500meg, and that will help too.