if all you really need is the support for 1080p, then you don't need a high end graphics card. you can get away with anything that has built in hdmi which i recomend on getting. i have a 3870 connected to 42 inch lcd 1080p with sound through one cable, which is most ideal. even cheaper hd 2600 had to the same task for $100.http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010380048+106792278+1067929475+1068309611&name=256MB
it comes with the dvi to hdmi adapter which you will need. it's single slot and should be easy to cool in htpc case. plus it has the built in high def decoders for blue ray and hd-dvd, so it doesn't overwhelm the cpu. with gtx you will get a lot of heat. if the ability to display on 1080p tv is ur only requirenment then i would definelty go with this. plus this graphics card uses very little power.