MSFN.org sends word that they've snagged Windows Messenger 5.0 Beta 2 Build 0230.

Keep in mind this is a version of Messenger only for Windows XP, with the added features of corporate IM functionality such as the SIP Communications and Exchange Messaging services which is not present in MSN Messenger. But... it doesn't contain the new features of MSN Messenger 6, so take your pick