CPU is plenty fast and so is the ram, old school RDRAM might be unpopular but it never was a slouch, was king of the P4 until dual channel DDR came into play. CPU speed is plenty fast, especially for an older chipset and ram. doubling the ram to 1GB might be good as well but then again it might not be wise to invest in RDRAM at all, 512MB should definately be enough for almost anygame, I think of it as the standard now these days although it certianly never hurts to be a step ahead.
I think the rest of the rig is fine and that the GeForce 3 is most definately the most influential bottleneck in the rig. A new graphics card could definately breath new life into games, but before you bite you really need to ask youself, "do I need this upgrade?" I say this because I compete online in games, and I usually don't need a new video card until I think my peformance might not be up to part or at least waning in light of other players and only if my frames could be a little smoother I could possibly be better and regain advantage I once had earlier on. That or I get new games that just run bad on my current rig, which is far more rare than the previous reason. I've gone from a 64MB retail 8500 on a desktop to a 128MB mobile 9600 and the difference is night and day. Not only does the 9600 allow me to play all of my previous games at 1600x1200, it runs them faster at that resolution than my 8500 could on a lower resolution such as 1280x1024 or 1024x768. That and I can play newer games smoother and actually can consider messing with AA and AF. Certainly is nice for a refresh but I could still more than survive on my 8500 if I needed to, and there are few new games that I'm actually interested in that my 8500 can't handle reasonably.