It's been awhile since I looked at the power usage of an xbox but for some reason I remember roughly 200W as being the number that the 360 and ps3 use. My new 32" lcd tv uses less then 60W so the game system will almost certainly use more then the display.
<edit> looks like closer to 180W
http://www.hardcoreware.net/reviews/review-356-1.htm </edit>