Css menu writer will only be in the WebAssist menu if you have design extender installed.
if you have the stand alone version of CSS menu Writer, it will be available under the Insert -> WebAssist menu.
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.