PIDGIN/Ubuntu - MSN/AOL and Microsoft OCS all in one

Well, while not as easy as it could be:

Install pidgin Internet messaging from "add remove applications"

Then get the pre-reqs for OCS:

sudo apt-get install autotools-dev libtool intltool comerr-dev libpurple-bin libpurple-dev pidgin-dev

Download pidgin plugin for OCS (if you have the older version there is no option for "Office Communicator is says LCS/OCS")

http://sourceforge.net/projects/sipe/files/sipe/pidgin-sipe-1.6.3/pidgin-sipe-1.6.3.tar.gz/download

unarchive it, then:

./configure –prefix=/usr/
make
sudo make install

Then to make it work, add a new account:
protocol: Office Communicator
username: email address
login: just the login name
password: secret password
Local alias: optional
ADVANCED: optional
(Connection type: auto, User agent is Purple/1.6.3)