Update:
After reading some of the TNet forums, it looks like there is a server executable included in the package (it's only 35Kb). You run that somewhere, and then connect to it. One person (usually the first to connect) becomes the authoritative player, but gameplay still goes through the server.
There is also a built-in ability to just "host" a game, but it still seems to fire up the server.exe behind the scenes and the person "hosting" again becomes the authoritative player.
There is a big thread on this here (this is page 2 of the thread where the server questions start, about half-way down):
http://www.tasharen.com/forum/index.php?topic=2513.25it seems like they're really going out of their way to make it easy to use, though that's just from what I've been reading. I wanted to hold off trying it until there was at least beginning Playmaker support for it.
One of the coolest things about this package (besides the supposed better data transfer rates), is that the server can be set to persistant, meaning that if the authoritative player leaves, another one automatically takes over. You can also save any and all scene data on the server, so the game can shut down and pick up where it left off if that's something that's needed. It appears that even if you shut down the server, everything gets saved and you can just start it up again.