Steve,
I'm pretty sure you can setup your firewall filters to block access on certain ports which handle the Instant Messaging traffic, but I haven't set this up yet (hoping I don't have to go that far with my users, BUT.....)
I'd like to know the answer to your second question - logging the IM traffic for admin purposes, to see who is using IM and see how long, what they are "chatting" about, etc.
Anybody have any ideas?? Thanks.
Regards,
Patrick