upgrade my system needs some advice.

ive upgraded my system to amd athlon xp2600 40gig 512mb i was wondering if i added more memory would it make any difference in performance oh i have a ati radeon 9600 128mb

I think nowadays, you should look to get at least 1GB of RAM. So adding another 512 would be a good idea. Won't do much for Live 2004, but for games like Far Cry and other new stuff coming out it'll definitely help the load times and prevent the in-game stuttering.
Make sure if you buy memory you buy the right type.