Select Usergroup At Registration

[Radon3k]

As the title implies, I'd like a hack that let's a user choose which usergroup they want to be in at registration. I only want them to be able to choose one, however. They can select another usergroup after registration if they want to. I did a search here on vB.org and found a few requests for this but it didn't look like anything ever came of it. Thanks.