Instant Messaging in the Enterprise

At work recently we needed to migrate from the Instant Messaging functions of Exchange 2000 to something else. After trying out a number of Jabber (sorry, XMPP) based servers, I finally decided on Wildfire (formerly known as Jive Messenger). This is a great server if you are running Windows rather then Linux, and has a brilliant web based interface for administration. Add in LDAP integration for authentication and it's one of the best you can have. On the client-side is a little different, but in the end we decided on using Pandion rather than Jive Software's Spark (their companion to Wildfire). Pandion just feels like an improvement to Windows Messenger 5, whereas Spark just feels 'different'. The only issue is that we can't get Integration Authentication to work. Pandion supports it as an option, but Wildfire has yet to support it - the good news is that it is a current feature request. The best thing is that these products are GPL'd, so you're free to use them.