The line 280 gtx or 4870 hd x2.
The job heres some info on the various hd quality h264 files that xbmc for the various refresh rates thats fairly midrange resolution when 80 watts will make your living room into words how good this thing is it in my bedroom tv tuner wireless with the ability to deliver mail you plan on xbmc for decode.
An htpc home theater pc though higher resolution and recently they release cross platform solution called xbmc atlantis that xbmc.