My daughter who is now 6 had a brief period like this about a year ago where she mistakenly thought it was a good idea to scream and pitch fits. Nuh-uh, ain't happening. I would grab her gameboy, go into the bathroom with her, tell her that she could pitch her fit all she wanted and I would talk to her when she calmed down. Then I'd sit against the door so she couldn't get out, put the earphones in and played her game until she was done. The first few times, she pitched a fit for about an hour, after a few times though, she eventually gave it up. After a few 5 minute rounds, she eventually got the picture that she wasn't going to win--I could just head in the direction of the bathroom and she'd stop.
Once she was calm, we discuss what she'd done and I'd tell her that as a result, she had to have a punishment. (no tv, loss of a toy, etc)
It completely changed her behavior altogether.
Just a suggestion. What works will differ from child to child, I'm sure. Just find something that works and be consistant. Hang in there!
