Why have you not played Psychonauts yet?
Seriously, it's only $10 or so, and instantaneous if you do take the XBox Live route.
You will thank me.*
* Only if you have a whimsical-yet-twisted sense of humor and would be unreasonably amused by blistering dialogue, brilliant art direction, re-appropriated psychobabble, and truly ecstatic luggage. One word: Lungfishopolis.