There was an issue with the file on the site. Please download again and you will get the .zxp. .zxp is used for Dreamweaver CS5.5 and above.
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.