If I were you, I'd use Dreamweaver to manage the designs of your page, then use Visual Studio to add the code. I wouldn't rely on DW for very much ASP.NET support. I'm not sure about CS4, but previous versions added their own controls etc, and offer no intellisense or debugging support.

You should really move away from relying on WYSIWYG web page designers anyway.  Trust the browser, not the designer.