In related news, Microsoft continues work on Windows Vista build 5381, which will be finalized as Beta 2 on May 22. Attendees of the Windows Hardware Engineering Conference (WinHEC) will receive Windows Vista Beta 2 on DVD, while Microsoft plans on seeding the build to testers, other partners, and millions of consumers via a widely distributed Community Preview Program (CPP) in the following days. If you've been waiting for a chance to get your hands on Windows Vista, that day is finally coming.
Source : Wininformant.com
To be Frank I had expected The Build would be in 54.x.x Series But still knowing that many a Time Thurott is wrong dont consider that 5381 will be Beta 2 For Now