Blocking Chat Programs & Social Networking Sites

We are trying to find a great solution to block all users except for management from Instant Messenger Chat programs like MSN Live Messenger and Yahoo Messenger. We are also looking at blocking all social networking sites like FaceBook, MySpace and Hi5 as most employees seems to be abusing the net during regular working hours.

Our Current Setup:
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(1) [ISP] -> [ADSL Modem] -> [Switches] -> [Server 2008]

(2) [ISP] -> [ADSL Modem] -> [Switches] -> [IP Phones] -> [Workstations]

Any ideas welcome.