Two main ways to do this.
- Server side coding...
- Get the ajaxcontroltoolkit from codeplex(http://ajaxcontroltoolkit.codeplex.com/), use the documentation to create a modalpopupextender (http://www.asp.net/ajaxLibrary/AjaxControlToolkitSampleSite/ModalPopup/ModalPopup.aspx).
- Add event handling on the radio buttons, and in your code behind, check to see if the combination is selected, and if so, show your modalpopupextender.
- Client side coding...
- Use jquery ui to create a jquery modal dialog box (http://jqueryui.com/dialog/)
- Use jquery to handle the selected event of the radio button input and if the correct combination is selected, show the modal dialog. (see jsbin samplehttp://jsbin.com/acupax/1/edit)