Does anyone know of a good Instant Messenger program that we can use on a 2008 Windows Business Server with terminal services?

I basically need one that would be available to all users, limited into inter-office communications only, and have the ability to keep a history? And ff its free, it would be even better, too ;)

Keeping a history of IM is a bit tricky and requires a capture and archival process (expensive).

Check into the Exchange add-in for WBS08. It is a full-blown MAPI email client that you can use for inter-office only or connect it to the Internet. It keeps emails and if you have to have that record in spite of what users delete, you can Journal all of our email to a separate mailbox.