The RELEASE CANDIDATE (RC) will expire June 1. However, it will auto-shutdown every two hours beginning March.
Two weeks before that, Windows notified the user that that's about to happen.
The BETA (any build before 7100) has already expired in 2009.
You cannot upgrade your RC copy with a retail version serial number, you will have to install a fresh copy of the full version...UNLESS you upgrade to Ultimate Edition and are willing to putz around with some files (I have not tried this, will not vouch for this to work):
http://www.howtogeek.com/howto/3075/...s-7-rc-to-rtm/