If we submit an Xbox 360 game, how important is it that we support 640x480? Because, my game has an inbuilt level editor, and with all the GUI and such 640x480 does not provide enough screen space (decreasing the size of the GUI elements would make them unreable on CRT televisions).

The rest of the game works fine in 640x480, it's just the editor. Would I lower my chances of winning if my game said "You need at least a 720p television to use to editor" yet it was still fully playable?

It is not important that you support 640x480 only; we do have a 720p HDTV connected to our evaluation system. You will definitely not lower your chances of winning if your game said "You need at least a 720p television to use to editor".

Ralf Herbrich, Microsoft Research Cambridge