That's the problem with DW. 4 neverworked with OSX. PHP support was lame either with PhAKT or ImAKT(sp?) which I purchased. ImAKT never worked in 4 with OSX.
I switched to GoLive6 as soon as it came out. It was native OSX and it provides its OWN library for PHP, JSP and ASP. Of course, I do not care about ASP. The php libraries are very good quality. Some of the built in features, such as being able to edit a list of records at a time are very neat. It comes with pre-built php/myslq and jsp servers to get up and running quickly. (Although OSX updates have caused some gyrations here, not really GL6's fault, just a matter of keeping up with a dynamic operating system.)
I would recommend you check out the user forum which is very OSX active, although php/mysql is not really platform dependent. There is a tryout version.
In comparison, the only real difference I miss is session values in the bindings palettes.