If I understand you correctly...
If you export your entire document, then yes, you will get a single image and images do not contain text.
If your goal is to have a background image and be able to align scalable text on top of boxes in your background image, then I would definitely choose a different approach. You'd need to be a CSS expert to pull that off.
What would be better is to export your background image without the boxes and then to come up with some way of placing your navigation above the background image. You could use a table or a div with a background color or a repeating background image and scalable text within the table or div. Why do you need your navigation items to be scalable? Many sites use images for naviation menus so that the design is fixed.
Whichever method you choose, you should do it in Dreamweaver. You'll be designing HTML or CSS, not graphics, so you'll want to look up tutorials under those topics, not Fireworks. Fireworks is not a Web page/site development program.