Yes, I have both installed right now. I have an NVidia in my AGP slot which is the graphics for my display, and then I have an ATI TV Tuner card in a PCI slot that I use whenever I feel like it. Should work fine.
I dont see why not lol. I mean a tv tuner card is pci last I checked and has nothing to do with the graphics card. I have a ati all in wonder 9700 pro and I am able to have a tv tuner in addition to what the card already brings. So I hope that answers your question