Can you give some idea as to what spec. your system is? ie CPU, GPU and Mother Board etc...
For most of us, 3 gigs is plenty.
4 gigs on your 32 bit XP will be overkill and even more so for 8 gigs.
If your system is a low end spec one, you might just want to stick to 2gigs of ram.
Even if you upgrade to 64bit XP, is the rest of your system going to bottleneck it?
ie like a 5 litre engine in a car with a small exhaust and weak drive train.
Games and graphic intense apps. would benefit from more memory.