The mac mini is a good idea and has been done successfully before. Check this out:

http://homepage.mac.com/peter_green/MacMini_Portable_Project/index.html
_________________________
PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...