If you haven’t already noticed, The Messenger Team posted about the new updates that users of Windows Live Messenger 8.5 Beta 1 will be prompted to update to Beta 2. While the updates will be optional for Windows XP/XP 64 bit/Server 2003, Windows Vista 32/64 bit will be forced to update to Beta 2, which ironically cannot be installed from the current beta installer that is available.
So for those that want to use the new beta and are using Windows Vista 32/64bit, install the Windows Live Messenger 8.5 Beta 1 and logging in will prompt you to update and accept.