Thanks to Khujo and iCe| for the heads up.
A beta build of MSN Messenger 5 has been leaked. It seems that MSN Messenger 5 will not be replacing the current Windows Messenger 4.7, but instead act as an alternative. Here is the message I recieved (which mentions the unreleased MSN 8) after installing the build:
Your computer has both MSN Messenger and Windows Messenger installed. Both programs can be set to connect to .NET Messenger Service with your Passport when Windows XP starts, but not at the same time.
If you regularly use corporate instant messaging or Outlook Express, you'll want to select Windows Messenger.
If you regularly use MSN services such as MSN 8, Hotmail, Mobile, or Chat, you'll want to select MSN Messenger...
Note: At the moment, it appears that it is impossible to log in using this version of MSN 5.
Screenshot: >>Click Here
Download: MSN Messenger 5.0.0317 - Windows XP (2.14mb)
This is BETA software!, please use caution when installing it on your system