I see everyones just confusing u so basically look at it this way.
RAM is the same as CPU's, graphics cards etc in the sence that the better one will perform better. It's as simple as that.
PC2100 is FINE for gaming but PC2700 is better and PC3200 is better again.
In the same way ur XP2500 is FINE for gaming but a XP3000 is better and a 643200 is better still.
Do u see what i mean?
Now i assume ur going to overclock ur CPU? If so, and as mentioned in a previous post above, u'll want some PC3200 ram BUT (and it's a big BUT) I wouldnt bother!
Yep u heard me right! Ur system is being let down NOT by ur CPU or RAM but by ur Graphics card so instead of messing round overclocking/buying more RAM i would just buy a new graphics card!