Sign up period will last at least 10 days. 1,000 people will participate in this beta. Everyone has to go through the beta application. Make sure they fill out "Why Should I be a beta tester" Sierra are seeking a wide variety of Tribes players from around the world for the test, from newbies to hardcore players. PII 300 or better beta testers will be tasked with faithfully reporting any bugs as well as playtesting Tribes 2.

update: Villain spotted a post on the TRIBES2 forum giving a few more details and mentioning http://beta.sierra.com/ and http://www.tribes2.com/ as places to signup when things get going.