When I first started developing dynamic Web Pages, I was working in ASP as well. I was not using Dreamweaver though, I was coding ASP in TextPad.
I started drifting to PHP about 6 years ago. I have found the transition form ASP to PHP to be fairly easy. The PHP.net website is very easy to use for looking up functions and getting code examples, much easier than the MSDN website. And the PHP community is very active and willing to help.