OK, after doing a research. I think I am going to get a GeForce 6800 (128 MB; AGP) for $165 - $175 (newegg) since it will only last about a year in my current gaming box. Then, get a new motherboard with PCI Express and a new video card. I will just toss the 6800 into my Linux box since it uses GeForce 4200.
I cannot believe PCI Express got popular fast. When I got this motherboard last summer (2004), it was not popular! Ugh!