I use PHP/MySQL on OS X (10.2.5) with DreamweaverMX - no problems (besides my lousy hand written 'extra' code efforts now and again)
I installed both MySQL and PHP by using Marc Liyanage's binaries and followed his install instructions to the letter (
http://www.entropy.ch/software/macosx/ )
I usually just use the command line to set up new databases - but PHPMyAdmin also does a good job. Then it's just a matter of setting the user name and pass for the localhost connection in Dreamweaver and it just works.
If you haven't already been to Marc's site, I recommend it whole heartedly.