[igalan]

Upgrading the graphic card is the best possible upgrade in your case. Changing the motherboard alone won't give you much improvement, because the processor, RAM and disk drives will be the same. Not to mention the fact that you'll spend many hours for a 1-3% improvement. Anyway a 3 GHz CPU is more than capable of running the newest games at the highest resolutions if it's paired with the proper hardware.

So if your motherboard is AGP, get a good AGP video card. ATI X800 XL or GeForce 6800, 6600GT with 256 MB RAM. If you have a PCIe motherboard, then the newer ATI X1800 or GeForce 7800 are current high end models. In your case swithching for an ATI gfx is very easy: unplug PC, open case, remove old card, plug new one, close and start. Tha Catalyst driver is already installed so the new card will be automatically installed.