I’ve tried this before and binned it due to the mess MSN creates on your googletalk contact list, but here I am again re-connecting my MSN Buddies to GoogleTalk…

Connect Google Talk to AIM, MSN, & Yahoo - BigBlueBall Forums
Now that Google has opened up their Google Talk servers for federation with other Jabber servers, you can use Google Talk to connect to your friends on AIM, MSN, Yahoo or ICQ.