Pop-up modal box when radio button clicked

Hi,

I’ve a form with 2 groups of radio buttons e.g. one group has 3 radio buttons  1, 2 and 3 and another with group with 3 radio buttons – A, B and C.

When a user selects a certain combination e.g. 1 and B, I want to display a modal pop-up with close button.

Can somebody give me a clue as how to do this? I'm new to asp.net so please explain step by step.

My web page is coded in c# asp.net.

Thanks

Joe Green