Tracking Instant Messenger on the LAN

Howdy all, thanks to any takers! 🙂

I am trying to figure out how to track Instant messenger messages passed via our LAN. Currently we allow the use of MSN, yahoo, etc. but the boss wants to know if it should still be allowed, and wants a presentation displaying the pros and cons. One of the ways I will show him is by creating a chart showing the amount of IM’s being composed for business, and the amount being composed for personal agendas. Any takers?

Thanks,
Sozo