I got the exact same computer for $12.50 at a university sell off. My computer has been horrible for games. A Nintendo 64 gaming console actually performs better. I determined that it's not worth upgrading it, except putting in another hard drive. Also the RAM on this is really expensive to upgrade. I needed solutions for my RAM and my gaming. I HAD to have some kind of solution.
I found this:http://www.techspot.com/downloads/4842-game-booster.html
I have run both programs daily, using WinXP, for about 6 months without ANY problems.
This should help you enjoy your computer much more.