The exit can be removed for sure with a dropdown box on the config. I'm not so sure about the green bar, but I think so with a different theme. You could/should post this in his forums, he is very good about answering questions.
Gameex isn't/wasn't really designed with standalone cabinets in mind. Tom's goal started off to make it an extension of windows media center edition. It has most of the abilities of other frontends, plus a ton of media center kind of functions, plays videos, displays rss feeds, streaming audio/video from the web, remote web interface to control/stream video/audio. If you want something that completely doesn't look like windows, atomicfe or mamewah might be better choices. Frankly I use all 3 and swap around all the time so my cabinet always seems fresh when friends come over.