The Radeon x1300 video card by ATI is possibly the best you can get for a PCI-slot graphics card.
However, the amount of money that would be spent on a Radeon x1300 PCI would almost be as much as a new motherboard. So what I suggest is that instead of getting the top PCI video card (which is still very low-end), that you instead get a new more upgradeable motherboard, which will cost almost the same as the x1300.
I strongly suggest that you do not invest in getting a nice PCI video card. The best PCI video card will be outperformed by an AGP/PCI-Express video card that costs less.
That would be my suggestion on what you should do, post back if you want some links.