I had to bump this thread to praise the powers of the Sheldon bolt trick. If you have a cup stop and read this post before you do anything else to damage it.

Go to the hardware store and buy 1 - 5/8" x 2" grade 8 bolt, 1 - 5/8" grade 8 nut, 1 - 5/8" grade 8 flat washer, and 4-5 5/8" grade 8 lock washers. You'll also need a deepwell socket, should be 15/16" and I'd use 1/2" drive. Google Sheldon Brown's bottom bracket bolt trick and use these items to prepare the cup for removal.

First try by it by hand, I've been able to get several out with an 18" breaker bar but I've had a few that were very stuck and my attempts yielded no results. If you run into one that's really tight find a friend with an impact gun and an air compressor, or just go to a mechanic shop. Have them tighten the bolt until it quits spinning, then have them hammer on it with the impact....it will come off. Most of the time when I've resorted to this I wished I had never wasted my strength trying to loosen it by hand. Makes me wish I had air in the garage.