No catch - I just need a valid e-mail address to send the invite to. Not sure what Vine is? I'm still figuring that one out myself at the moment.
You can read what Vine is about here and check out the FAQ.
If you are looking the the latest version, as of today (05-20-09), version 1.0.2151.0, download the binary from here.
Earlier versions (1.0.2150.2/older) would sometimes crash when the update to v1.0.2151.0 was offered. This avoids that situation, which could get annoying.
The Vine also has a dedicated TechNet forum located here.
I'm guessing there will be more to this program once it gets closer to a full blown public release.
Update: I've seemed to have run out of invites because when I invite people now, they get sent to the sign up page for the waiting list. Either they are at capacity right now, or I've given out all I can for now. I will update when I have more info.