Need suggestions for HTPC+Sharp Aquos 1080P HDTV

Obviously I'm new here, but in doing my research for my htpc this seemed like the place to get my questions answered.

I'm using my older computer (sony vaio) as a basis for an htpc. I have a sharp aquos that I just got (46 inches). I need a recommendation for a pci graphics card, I know. Unfortunately the mobo only has a pci port. It needs to be able to play games reasonably and output to 1920x1080 resolution and still look and perform well.

The only other option I have at this point is that I have an x800xl 256mb pci-e card laying around and I could try and switch the mobo out. If so I would need to find a mobo that supports the pentium 4 ht and pci-e, which is also rather difficult. Any help would be great because I am not quite sure which route is better and what would work on my aquos. Again I would like to theoretically TRY to placy some newer games and be able to surf the net/watch dvds/listen to music on the screen of my hdtv and have it still look good/run well. Thanks in advance!!