Taking screenshots on the Samsung Galaxy S 4G?

I cannot for the life of me figure out how to take a screenshot on this phone. It's the Samsung Galaxy S 4G for T-Mobile, running Froyo 2.2 I can do it with the SDK programs when the phone is connected to the computer, but I want to be able to take a normal screenshot with the phone. "Back + Home" does NOT work on this phone, nor does "Back + power." There HAS to be a way! Anyone know?