Due to popular demand, we've decided to keep Sins of a Solar Empire Beta 2 open until July 31st. Anyone who pre-orders the game in July will gain immediate access to Beta 2 and all subsequent betas before Sins' final release in February 2008.
Your forum account is the same thing - it works across all of Stardock's websites. You don't need to make another.
If you want to get into Beta 2, you can pay $69.95 to become a TotalGaming.net member and receive 10 tokens. You can then spend 5 of those for Sins and immediately download the beta, all future betas of the game, and the final version.
Or, if you want to wait for Beta 3, you can use a credit card. You'll be charged $44.95 when Beta 3 is released (you may see a hold on the funds for a few days, which depends on your bank).