Jet, If your ignition hasn't been giving you warning signs that this would happen, I'd reccommend taking some time and jiggling both keys in the ignition trying to get it to turn.
Most of the old cars I get with stuck ignitions, I can usually get to turn after working at them for 10-30 minutes. It just takes a lot of patience! Wiggle the wheel as well when jiggling the key. Its a much easier than spending a few hours (and less messier) than drilling or sawing it out.
On my 87 300D however it got stuck in the opposite position. I finally got the key to turn and got the car started, but I couldn't turn the key off. Pieces of the steering lock fell out from underneath. I could take the tumbler out, but couldn't get the lock to turn. I had replaced the tumbler a month before hoping to prevent this. I eventually got it out by breaking the exposed internal parts out (behind the tumbler) and then popping the lock.
hope this helps
