Like the boys said, we need more info. I wouldn't rush out and buy more memory just yet. 1 GB is likely enough for an XP system assuming you aren't trying to run too many other things at the same time.
Firstly, what processor are you running? That may well be your bottleneck.
7 Series graphics cards vary widely in performance - do you know which model you have?
Also, what resolution are you running your monitor at?
Cheers
Wooley