You should probably have them in two different forms since they function as two different forms. That way they can share the same named form elements and won't have issues with blank values.
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.