Before buying ram try this:
Go to HERE
and run the Crucial
This will give you the exact memory configuration for your system.
You do not have to buy the memory from there, but write down the information and if you need assistance in purchasing the upgrade memory GTG can assist with suggestions also.
I would upgrade to at least 1 gig of memory. That seems to be the so called sweat spot for XP.
Check the suggestions Crucial gives and if you need help let me know and I will check the previous website I gave you for the price on upgrading ram to not only 1 gig but more if possible depending on the price.