Hello Sutiban,
I was not involved with the Vista Beta program and I really don't have any idea who you could contact about that.
My only suggestion would be to post your question in one of the Vista Newsgroups http://go.microsoft.com/fwlink/?linkid=42486, maybe there is an MVP or someone else that had the same issue, that could help you out.
Sorry I couldn't be more help,
Darin Smith
WGA Forum Manager
p.s. If you still have a computer with (Vista installed) that is using one of those keys, there are programs out on the internet that allow you to see what the key being used, is. Because of MS policy, I can't provide you the names of the programs, but they should be fairly easy to find.