Muhammad Umer pointed me in the direction of the following statement posted quite a while ago on the Windows Vista Team Blog. It's something we haven't covered but pretty important if you downloaded the CPP (Customer Preview Program) of Windows Vista Beta 2.
It was understood that if you registered a key for Beta 2 you would automatically be accepted for RC1 when it ships, this appears not to be the case. Participants will only be inviited to download RC1 if you have activated your copy!
This from the Vista Team Blog:
"Please let us underscore a very important point surrounding Windows Vista Beta2 that can be easily overlooked in all the excitement to download and install the code: it is very important that every user activate Windows Vista Beta2 within the first 14 days of installation. Activation allows us at Microsoft to test our support infrastructure as well as the activation process itself. In addition, we'll be unable to provide you with a copy of RC1 (Release Candidate 1, the release subsequent to Beta2) unless your copy of Beta2 is activated."