Ditto on jbmadtown's response. The paths are great. I live in Fitchburg and commute to downtown Madison on the Capital City Trail every day. I commute with deer, hawks and woolly-bear caterpillars. There are a few days when the snow piles up and doesn't get promptly removed, but normally, the paths are rideable.
My recomendation is to get an old second-hand wheelset and put a set of studded knobbies on them. On icy, snowy days, pop the studs on and let 'er rip.
I'm not sure if you're coming from out of state, but if so, here's a partial list of organizations you might be interested in:
Bicycle Federation of Wisconsin: http://www.bfw.org
The best $25 you'll ever spend on cycling.
Wisconsin Off-Road Series: http://www.wors.org
The biggest off-road racing series in the country.
An outstanding citizen road-racing series.
Good luck with the move!