The 2 are pretty unrelated. If you mean you use DWMX as a WYSIWYG editor, then you should understand that PHP does not have any WYSIWYG functions whatsoever.
Apart from that, there really is no connection. DWMX doesn't have that much in the way to offer for PHP support. It handles syntax coloring OK, but there is really nothing worth putting in a book about it. There are no real tools beyond your mind.
I have also used Primal Script and Zend. Both are superior to DW, but they also have their quirks. Zend is just tremendous, but it is also extremely laggy. I would use nothing but Zend if it didn't run like sh*t (PIII, 512 MB RAM, 800Mhz).
