If it's REALLY rusted stiff, then you could try either 1 pound of c4 OR a 12KW co2 laser. Bear in mind, though, that these are both outdoor procedures.

Actually, I agree that you should just get a chain tool. If you are seriously low on cash, then (I can't believe I'm recommending this) you can get one at wal-mart for about $3. Don't use the wal-mart tool on the rusted chain, because it's a total piece of crap, and will probably break (use the aforementioned cutters for the rusted chain). It should suffice for installing the new chain though. As soon as you can, invest in a good chain tool - you won't regret it.