Traffic monitoring and traffic blocking

What’s the best way to find out what kind of traffic is going out (and coming IN) across a T1 or serial link? I need to find out how much of the available bandwidth is being allocated for RealAudio, RealVideo, MP3 downloads, etc. Once this is determined, what’s the best way to block RealAudio, RealVideo, and other streaming media without blocking access to applications that utilize UDP ports about 1000??