Servo Magazine is running an article in their Nov 2006 issue on the Roboreptile which is part review, part hacking mod. The writers initially thought of hacking the hyperactive dino to breathe fire, but then thought better of it (melted plastic doesn't smell too good), and decided to go with smoke-breathing instead.

Their 'smoke' source is compressed CO₂ and they hit on the idea of cannibalize a paint gun which has a CO₂ cynlinder that is small enough to hook up to the Roboreptile. If you're into hacking, then this is a fun little project, and the guys cover enough of the details so as not to leave you hanging. Unfortunately, the article isn't available on their website, so you're going to have to go out and pick up a hardcopy. Have fun!