Take a 50cc scooter, get it out into the snow, now bolt on a front ski instead of a front tire

the Slidescooter was dreamt up by RiminiMoto, otherwise purveyors of fine Honda Cub accessories. Their approach really isn't more complicated than the above. The snowboard-like front track uses a ski-like snowboards cut down to fit, to provide some directional stability. It's connected to the front forks by a support that bolts in right where the axle would normally go.

http://hellforleathermagazine.com/2009/01/slidescooter-taking-the-piste.html via an article I read in Men's Journal