Hey Chad, welcome to insanity! I think we emailed back and forth through the badgerlandrovers group a while ago.
Anyway, to answer your question, there really is no legal, public land offroading in SE Wisconsin. Lk. Geneva Raceway has some trails, with an interesting mix of mud, trees, and sand, but it's private land and the owner charges ~$300 to open the trails -- even if you only have one or two trucks I'm told!
Other than that, you can drive to Attica Indiana (Badlands ORV Park), or the Pipeline/McCauslin Mtn. up near Mountain/Lakewood WI (about an hour north of Green Bay); there are some trails near Black River Falls; and there is "The Cliffs" in Marseilles Illinois (about an hour south and east of Beloit).
Andy