Checkboxes will allow for multiple selections within a group. If you would like to limit the user to make a single selection you should be using the radio group instead.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.