It is generally better just to upload the files after editing to your wordpress site and preview live in a browser.
WYSIWYG editors are generally poor ways of developing sites as they often add a load of bulk code, some of which is not standards complient.
I use MS expression web (similar to DW) but only the code function of it as it has great code autocompletion. I then upload any modified theme files using filezilla (free) to my site to see the changes.
It is actually a very quick and good way of doing it as I just go ctrl-s and then drag the file over in Filezilla.
Also review some of the information available in Templates.
my workflow is this:
i create a bunch of relevant HTML templates in dreamweaver. mainpage, category, post, archive, etc.
then i create a new site on my localhost (WAMP server), copy all the WP files into it, create a new theme folder and start copy-pasting the relevant blocks of code into the PHP files. i can see them live in the browser on my localhost.
after that i start inserting the relevant WP code snippets.
if for some reason you can`t install WAMP, then use the online server to test the files the same way. just create a FTP connection in DW and check “upload files after saving”.
I work the other way around:
I draw a sketch on a piece of paper, install Starkers Theme for WordPress, which is completely naked (although it needs some minor tweaking for 2.8.x), and start building the css.
Peter