I'm have that set up as a secondary HTPC running Windows XP MCE2005. For a TV Tuner, I'm using an ATI All-In-Wonder X1800XL. I'm not having any problems with it. It should run modest games fairly well when paired with a mid-range graphic card. I'd say nothing above an 8800GS/9600GSO or maybe the HD4670, otherwise you start running the risk of a CPU bottleneck.
(Note: I was running an 8800GTS-640 with an X2-4800+)