PowerColor’s half-height Radeon HD 5750 launched a quest to build a tiny gaming PC. But things didn't work out the way we planned. We ended up building two half-height machines capable of cranking out playable frame rates, and put them both to the test.
Tiny nettop HTPCs are great for playing back HD video, but they aren’t able to tackle demanding games at high resolutions because they lean too heavily on integrated graphics. We've always been intrigued by the possibility of a tiny PC that can handle media playback in addition to late-night frag fests, so when PowerColor introduced a half-height flavor of its Radeon HD 5750, we got excited about the possibility of squishing significant graphics power into a tiny PC.

With 700/1150 MHz core/memory speeds, PowerColor's Radeon HD 5750 runs at AMD's full reference specification, despite its half-sized PCB. The only physical feature that betrays its power within is a dual-slot cooler.

We’re well aware of powerful gaming PCs that use the small cube form factor, but we want to see if we can push the size limit even harder. Can we build a machine capable of gaming at 1080p as small and thin as the new, slimmer Xbox 360?

We know that smaller systems require careful planning. Even when we put our System Builder Marathon machines together, we run into compatibility issues--and that's with full-sized ATX platforms. The smaller you go, the more complicated things can get, though. What we didn’t know--until we tried--is that a successful half-height build can be far more involved than you might otherwise imagine.
I've been using this one in my main HTPC for a couple years now at least. Haven't had any problems.
AMD Phenom II X4 705e isn't it x3???
Many small mini-ITX cases do include a small PSU, but what if you want to mod the PSU, or the included one breaks down? Falling back to standard ATX PSU would have to use a bigger mini-ITX case.
Too big? The PC-Q07 only has a single slot for the video card, but that would take the single-slot HD5770 that XFX makes: http://www.newegg.com/Product/Product.aspx?Item=N82E16814150501 . Both cases will take a full sized ATX PSU; I would suggest a modular one, such as the 550W Antec Truepower New I am using in mine.
Link to by baby
There are also plenty of half-height NVidia GT 430s out there http://www.pricewatch.com/gallery/video_cards/geforce_gt_430
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129040
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129039
Personally, I went full height and have my "gaming" htpc in a Fusion 430 Black
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129054
That case takes full height cards and full ATX power supplies. I have a 4890 in it with a Corsair HX650 and an Asus P5Q-EM with a Q9550. You could easily get one of the x58/p55 motherboards that supports SLI/CF too to get some considerable power into that footprint