I used to read the PC Extreme mag and in there was a whole section deicated to case mods every issue. One dude built a modded one into a briefcase, another into a teddy bear, a phonebox, a case with a turbocharger from a car, little servant robot, monitor etc.
Doing a briefcase one wouldn't be exactly cheap if you put a small LCD screen into the cover, but it should be ok if you just want to use it as a case.