It's a 16:9 PC monitor, but the type of TV isn't really relevant because I'm 1:1 pixel mapping the 360's output. A 4:3 640x480 signal is coming out of the 360, but for some reason the game doesn't fill 640x480, despite being rendered at 640x480. The 360 is conducting some kind of 'scaling' internally and messing it up.
UC2's rendering resolution is 640x480.