A forum thread on the TribalWar Forums offers details on plans for TRIBES Vengeance closed beta testing, describing the process, and pimping pre-orders as the way to raise your chances of participation from 1% to 100%:

Closed beta is simply a small link from "no beta" to the "open beta". We're using it to iron out major issues, and get the game to the level of stability required before starting open beta. There are certain issues you simply don't want to try to fix while 50,000 people are bitching that they can't play. Closed beta will let us fix all of those early.

Closed beta will be very small. We've had over 10,000 people register for the beta so far, and there doesn't seem to be a slowdown in sight. We will have less than 250 total openings in the closed beta until the Tribal-Wars LAN in late July. Of those, I've already filled about 100, which leaves 150 for those of you who are still hoping to get in. With my current database, that gives you less than a 1.5% chance of being selected. By the end of the week I estimate that your chances will go down to well below 1%.

However, if you want to take part in the beta there is a way you can have a 100% chance of getting in. Go to your local EBGames, or GameStop and pre-order (Marweas did it at Software Etc for $5) and then register for the Tribal-Wars LAN. Bring your receipt and you'll get a beta CD and you'll be in. I highly suggest that you do this now, because once the T-Ws spots fill up you won't have any way to get into the beta.