Dreamweaver allows you to create templates that can be applied to multiple pages. You simply create a template for one type of page layout, and then you can use it over and over for as many pages as possible. When you make a change to the template, it gets applied to all the pages using it.
I personally use FP includes.. very handy. I update one file, and every page is changed. I realize this is a crappy way of doing this, but I haven't taken the time to learn PHP yet. Yes, I know I should.
Michael Glenn Wendt