Auto assign user to group

[arasef]

We are using our forum to help track beta testing of our game. When users register, they have an opportunity to select a Yes/No radio box: "Participate in beta program". If they select yes, I want to auto assign them into the Beta Users group. It would also be cool if an auto mail is generated welcoming them to the Beta Users group.

Is there an easy way to do this?

Thanks!