Pete, the answer depends on how good a web-page you want, and how much time you're willing to devote to it. If you need to throw something together quickly, then Imageready may do an adequate job of outputting code for you. But it will definitely not be optimized code.
There are a lot of tricks that a coder can do in HTML that you won't get from Imageready. For example, using a repeating image for a background to save download time, or creating a fluid-width layout that will fit any screen resolution.
So if you're willing to spend the time on the HTML and CSS, then yes, it's definitely better to do it in Dreamweaver; but if you're starting from scratch, the learning curve is steep, so don't expect it to happen overnight.
Hope that helps!
Arvana
arvanadesign.com