Could this be possible with say an automobile lcd sreen from a dvd player?
yeah, i've done it. you'll need to build a video out mod though. google "atari 2600 composite video mod"
I've seen people do this with commodore 64's aswell.. For prophet/mssiah64
You should try and go bigger than 7" otherwise your going to have a hard time doing anything else than playing simple graphical games...
here's some info on modding a psone lcd screen to rgb input - my mate did this so he could have a portable amiga600 :) http://www.papayalabs.co.uk/hacks/psonelcd.php
well i say 'portable' it was really semi-portable and just meant he didnt have to lug around a big old monitor *grin*