Keylight is a powerful tool that should offer the results you're after. It's not the only option, of course. Primatte Keyer is just as powerful, with a completely different methodology (updated with 7.0). (The book's DVD-ROM includes a demo if you want to check it out.)
The next chapter offers hands-on advice for situations where keying can't help, or can't do everything, and rotoscoping is necessary.
Rotoscoping and Paint