First BIG mistake is running with the assumption that Fireworks will make HTML that can actually be used in a real world, working ,web design. It can't.
The HTML that Fireworks generates is absolutely awful from a functional standpoint. It's okay for a "mock up" to show clients... but it stops there or you're just begging for trouble, like you have now.
Use Fireworks or Photoshop to create your graphics. Slice them if necessary and then copy them to your root folder. Using HTML and CSS, design your site to accomodate your graphics. If you're looking for a multilevel menu, there are plenty out there that use Jquery (Smoothmenu from Dynamic Drive for example) or pure CSS (purecssmenu.com). Do not expect that a graphics editor is going to write and export a working drop down script. It was never desinged to do that. Dreamweaver is for HTML, Fireworks is for PNG and GIF graphics.