[UPDATE] 2009-03-13
Happy Friday the 13th. Just an update to this story - the SIPE plugin has been worked on by a number of great people including Gabriel Burt from Novell among a host of others. It is now stable and can be used with recent versions of Pidgin.
Check out their great work at http://sipe.sourceforge.net/. The source code can be downloaded at https://sourceforge.net/projects/sipe/files/
[End UPDATE]
OK, so I've been hacking the code for SIPE to get it working with Microsoft Office Communication Server 2007 and I've got it logging it but it's stuck at getting the buddy lists.
You can download the tarball here: siplcs-20081009-logs-in.tar.gz
Eventually I'll be putting up a read-only Subversion repository for all the IT Nerve Center code so you can check out the latest.
Enjoy,
Flux.