What do you use the computer for the most? That will largely affect what you should do. Seeing as you only have 1 GB of RAM right now, that might be the best way to go, so that way you won't need to worry about doing all that stuff with your CPU.
But you should say what you use the computer for before anyone gives any decent reccomendations.
Good advice all around... the reason I'm considering upgrading is to play OBLIVION better And the ram might help with the constant loading... but I play a lot of hl2 also. Of course, I could just save for later... but I'm bad at that.
depends what game you play, when i switched out my 2500(3200) for a 320064(4000) i got a nice fps gain in hl2 as it is very cpu intensive.
Still, it's not bottlenecking the card. It's the game itself that makes too much use of the CPU that's all. Lowering the resolution and enbling more IQ settings would tax the card better, thus taking the burdain off the CPU.
Oblivion looks impressive, but I'll bet you its going to be a resource hog graphically. I doubt a 3 ghz processor is bottlenecking that card much if at all, IMO the 7800 GS is basically a PCIe card thats been gutted and thrown into an AGP package anyway. I'd save your money and wait until you can afford new components , but that seems to be a common response on this forum. If you're going to spend the money now I think you'd get the most benefit from adding more ram. Windows will like you a little more and games like bf2 will benefit from it.