Hi, welcome to the forums! If you do a search for "jabber msn" you will get some helpful results:
http://www.internettablettalk.com/fo...ght=jabber+msn

The guide that I followed is this one:
http://www.internettablettalk.com/fo...ght=jabber+msn

If you're already on the OS2008 Beta release you should know that there is a bug in the fullscreen keyboard that causes it to not let you enter passwords correctly. The smaller "stylus" keyboard is unaffected.

Good luck and have fun with your N800!

-John