I have IM running. The user logon by default is username@servername. If you look in the user properties in “Active Directory Users and Computers” on the “Exchange Features” tab, double click “Instant Messaging” object. In the “Instant Messaging User Address” you will see what there logon is suppost to be. For example mine is ebellardino@baiserv1.
FYI: the newest version of MSN messager that with Exchange2000 IM is version 5.0 for Win9x & 5.1 for Win2k and up.