What are some options for security when it comes to IMing in the work place

Help desk recently caught a the spreading msn picture virus. We promptly got rid of it, but now my boss wants us to find out some things.

1. Some sort of way to use CA solutions (we have antivirus and monitor) to scan incoming files(specifically from messengers)

2. If there is a utility to “lock” the friends list in MSN, whether it be a add-on or MSN function.

Essentially just having to where you can only IM people inside the office and all incoming messages from foreign screen names will be blocked.

I was wondering if there some other instant messenger we could use that also links with outlook for mails that would give us advanced security options. Any help with the situation is Extremely appreciated.