Thanks for the responses - I'll post an example of something I may do with a piece.
First, though, what constitutes for commercial use? If my site has ads on it, and I'm only using the screenshot as a link or part of the design, does that represent commercial use? Or do I actually have to be selling a product that's incorporating their screenshot/concept art?
Ignoring how bad it looks, here's an example. I cropped the original and added a text overlay (which I would probably end up just doing in the HTML, and the image would ONLY be cropped)
Mine:
Original:
http://gearsofwar.xbox.com/MediaImag...e3_2010_10.jpg