Glad that You found my website! (http://hometown.aol.com/nuckem/index.html) We currently own 8 Snorunners and all are up and running.
SnoRunners are quite a lot of fun. They use the Chrysler Power bee 134cc engine that produced 7 hp. Of course, there are mods that can be performed to bump up the hp. Or, you can adapt a US Motor 820 Go Kart racing engine that puts out 11 hp.
SnoRunners perform pretty well in under 8" of snow, but tend to bog down in anything deeper. Of course, it depends if it's a dry snow or a snow that packs down. One of their limitations is that they appear to always have carb related problems from venturi icing to just needing a rebuild.
I think the Moped/sno-ped idea sounds pretty good. I'd guess it's an easy adaptaion for a front ski, and the rear could use a homemade type "paddle" tire, kinda like sand racers use. I'd love to see what someone comes up with!