Oh boy, I was hoping not to have to bother you with a reply...
"Go to Window -> Server Behaviors to open the sever behaviors list."
"Double click the Server Validations server behavior."
I don't see such a thing. All I see are the dynamic text fields (name and email, I took out the 3rd)
Attached is a screen shot of what the server behaviors panel says and what the dropdown inside that panel says.
I am happy with just client side validation on the radio group, but maybe you cannot mix and match client side and server side in one form??