Looking at the pictures of the Snorunner ... I think one could be built from a regular moped frame. The tracks shouldn't be too hard to put together in place of the rear wheel and the front woul just look like the Snow-ped Dan and Simon put together for the sledding race. The engine looks different, but I don't see why a regular moped engine wouldn't work (then again, I'm not at all an expert on this).
Why not get some junked mopeds and rebuild them as snopeds? That would be awesome.
Also, some schematics on the Chrysler Snorunner would definitely help.