Once the beta begins, you will have VIP access to the game, a 30-Day Active Booster, and 800 Tribes Gold.
Boosters usually entail more XP gain and the currency they are referring to could be used for equipment. I will see once I get into beta on the 4th. It looks like once you have preordered, you can start downloading the client but I'm at the office right now and cant further investigate that. But, I'm very excited to see Hi-Res is getting this done as they said they would! I've enjoyed their free to play model for Global Agenda and look forward to the new Tribes!
For those interested in Tribes: Ascend, here is the link I got from their email to preorder it.
For those not familiar with the Tribes series of games, they are a First Person Shooter that allowed you to jetpack and ski around. There were vehicles to fly or drive on the ground as well. Based on the gametype, you were either doing deathmatch, capture the flag, king of the hill style play, rabbit, head hunter, etc. They were strictly multiplayer save for Tribes: Vengeance which was a big flop :-\.