The basic "how do I convert an old road bike to single speed/fixed" thing has been asked a lot, though sheldon has the best stuff on it. To be Chicago-specific, the best source for raw materials is working bikes. We sell fixed up bikes at the storefront, but if you come by the warehouse and we're not too busy we'll sell you an as-is bike you can fix up and convert yourself. If you want single speed with a freewheel, all you need is a bmx freewheel and the patience to redish the rear wheel, so any shop can hook you up. If you want to go fixed, you need more hardware, and yojimbo's garage is the best source for that. PM me if you want more details, I volunteer at working bikes and will probably be around this weekend.