Popup with message when you hit the "register" button.

[Bob de Bouwer]

Hi,

Maybe there is a plug-in for this, or maybe someone can help me how to set this.
What we want is the following:

When people navigate to our forum and want to register, we want a "popup" shown first with a message.
So when the click on the "register" button, first a "popup" comes up with the message.
They can close it, and then register.

Does anybody know if there is a plugin that does this?
Or does anybody know how to set this?

Regards
Bob