Beta testing closed, no way to get a key, unless someone is willing to let you use theirs. You can install on 10 computers once you have the key. (MS email: You may install Beta 2 on up to 10 PCs using the same Product Key.)
This is the Microsoft site:
Thank you for your interest in Windows Vista. The Customer Preview Program is now closed. We have reached our program capacity and no new orders are being accepted. We apologize for any inconvenience.
For registered customers who have received a Product Key the download sites will remain open until Friday, July 14.