If you used the photoshop export as html feature you will have problems. All I can suggest is that you convert it to a css based layout, see -
Graphics apps generate code that is too rigid to work with. You'll get much better results if you use Photoshop for Images Only. Use DW to build your HTML and CSS code.
Recommended tutorials by people who know what they're talking about:
Taking a Fireworks (or Photoshop) comp to a CSS based layout in DW
Part 1 --
Part 2 --
Creating your first web site in DW CS4 -