Don't laugh, but why do you want to do this? You lose so much screen real estate it's funny! Graphics cards (my old ATI Mobility Radeon 9200 and my nVidia 8600MGT) come with driver settings to let you display images without stretching, BUT only on LCDs, for digital stuff like built-in displays or over DVI.
High-end CRT monitors will also let you input, say, 1280x720 and letterbox it for you, I saw this on a 19" samsung crt back in 04, it was selling for $300 or so.
But if your pc can play dead space, why no widescreen? A 17" one at walmart should be dead cheap!! I just give up with these silly x360 ports, they all run like crap, all except bioshock.