Any e-mail will work, but you'll have to make a googlewave account either way which will also have tied to it every other google applciation under the sun including gmail.
We're starting to run low on invites, so when the ones we've already used get approved, then we'll be counting on all of you who get invites when you come in to invite a couple more ng users.
Just post here, I'll add you to the wave and you'll have a list of who is waiting for an invite.