In yesterday's post I raised the impression that I downloaded Vista beta 2 and its product key from MSDN. I have to correct that, my beta 2 was obtained on the Vista beta site (no link, it's not public :(). This site uses the same download tool as MSDN but is not as chaotic as the new MSDN site (I'm still not used to it..) and a lot faster. The MSDN beta appears to be still beta 1. Which explains why my key did not work. The beta on the beta site is the same build, 5219, as the one in the PDC goods.
Sorry about the confusion.