You already have a PCI GF2MX? If so I recommend you stick with it until you upgrade your system. The PCI Bus is too much of a bottleneck on a video card, wait til you can get a decent AGP card.
You could have a Geforce4 Ti 4600 on your PCI slot (if they made one in PCI) and it probably wouldn't be that much faster than what you have now, because of the bottleneck.