With the new cat out of the bag, getting the AMP stack running is a little different on OS X Mountain Lion 10.8 Preview 3 than is its predecessor OS X 10.7 Lion, here is the lowdown on getting Apache, MySQL, PHP and phpMyadmin running on the new OS.
Apache/WebSharing
The first difference in the new OS is the dropping of the GUI option to turn on Web Sharing in the System Preferences, it may be gone but Apache is definitely installed in the lower level of the OS and ready to go.