sounds like if you have a HDMI output, your G2G, maybe not even that.
To test to make sure the new vid card was working right, I watched a DVD on an old P4 system with a 8400gs PCI vid card
My HTPC is a dual core AM2 @ 1.9 ghz with ATI 3200 OBG, and it does 1080p Blue rays no problem. I don't remember if I ever tested it with my 1.6ghz sigle core, but I was planning to use that one on my HTPC, and my research was sugesting it also wouold have been enough for BR
so, what you want takes very little cpu because modern low level vid cards have been optimixed for video playback.
The wife's laptop with intel 965g based graphics can play DVDs, but sometimes has problems with it. AVIs and MOVs have loweer requirements than DVDs