I don't know much about the roads up there (I live in the Racine area). I did ride the trail back in 2006 though. We parked in Grafton at a park along the river. Plenty of angled street parking and clean rest rooms. Here is a link to a birds eye view of that area (from Microsoft's Live Search Maps / Virtual Earth). Road the south portion all the way to Brown Deer Road first. Then headed back to eat lunch in Grafton. After lunch we headed north till the end in Cedar Grove. Then it was back to Grafton.

It looks like the extension to the Oak Leaf Trail is going to be started this year.
http://groups.yahoo.com/group/milbtw/message/5599
http://groups.yahoo.com/group/milbtw/message/5571