The CSS and Images export in no way excuses you from having a solid grasp of HTML and CSS. Once exported, you will doubtless have some tweaking to do in DW or your preferred web page editor.
There is also a very specific workflow for generating successful CSS layouts from Fireworks. Make sure you are comfortable with this workflow. You will find even then that knowledge of CSS and HTML are important even when following this workflow.
While it is written for CS4, many of the innovations that Matt Stow introduced here were added to the export script for CS5.
These videos by Dave Hogue are also excellent: