Network Monitoring?

I have been assigned the task of figuring
out what programs are running on the network.
The VPs want to know if our single T1 will be
adequate for the (soon to be) influx of web based traffic. They see everything from
people surfing things likecnn.com to xxx.com, playing network radio stations, and things like ICQ, AIM, webshots, etc.
They would like to pinpoint what is actually running & who is running it. They would also like the ability to block such traffic. Any info would greatly be appreciated.