A. For any beta of Microsoft software you can e-mail betareq@microsoft.com telling them why you want to be on the program.
If you have Microsoft sales or support contacts (e.g. a TAM for Premier Support, then approach them).
You can subscribe to Technet Plus which includes many of the beta's - these CD's are shipped/refreshed monthly.
If you subscribe to MSDN Universal then some beta's are shipped as part of this subscription.