margo, there is a date in the email... ive heard that it will say something like:
"* The official testers' site will become available for login on
*day, June *, 20**.
If you are unable to log in, please try again later."
this is when your account will be activated for the beta. You can then log in, and download the client. though this is all rumor and i have no evidence to back this up ;D