Shoutbox

Actually, it's Windows Live Messenger that permits a second connection to the same account.  Messenger Plus! Live allows you to sign into multiple accounts from the same location.

Unfortunately, the MPoP (Multiple Points of Presence) feature of Windows Live Messenger only works when using the main client, signing in on any other clients or ports of it won't allow you to remain signed in.

Also, please be clear in your terminology.  Windows Live Messenger (WLM) is a chat program (formerly known as MSN Messenger) made by Microsoft, Messenger Plus! Live (MP!L) is an add-on for Windows Live Messenger which adds some extra functionality and features