There are plenty of places to go cross-country skiing in Ann Arbor. Not many places to go downhill, though.
You could start at Bandemer Park on the B2B Trail and head through Barton Dam along the train tracks.
Or you could drive out to the University of Michigan's Radrick Farms Golf Course on Geddes Road.
Near Ann Arbor, there are x-c ski trails at Hudson Mills Metropark north of Dexter.