[Suicide Junkie]

Or why not just a bootable CD?
With a decent amount of RAM, you don't even need a harddrive except to store savegames and preferences, and a USB stick covers that too...

Either a cheap 64meg one for savegames, or a big 2gig one and have the game come on the bootable USB drive.

Its an easily portable game and a security dongle all in one.

The downside is no alt-tabbing out to chat while you play.