I had the same problem you did, couldnt justify the motherboard upgrade for the pci-e card.
anything in the gefore series starting with 6 has the calls required to get everything working. infact im using the onboard 6150 that comes with the asus motherboard in the video.. the motherboard cost the same as the graphics cards i was looking at, add in another 50 bux for a dual core cpu, and recycle everything else.
my machine is now running quite well. just got to find a nice dvb-t card that works with it.