Thanks Bink for the heads up
A new build of Windows Messenger 5 has been released to Betaplace for Greenwich RTC (Real-Time Communications) beta testers.
Along with this build Microsoft released the Release Candidate for their re-branded "Microsoft Office Real-Time Communications Server 2003".
The release notes state known issues for this current build such as:
The installer is 8.4 Megabytes in size.
Download: Download Windows Messenger 5.0.0292 (Must be a Greenwich RTC Beta Tester, login required)
News source: Betaplace.com