First install pdo.
I already had php 5 with the pdo extension included in the build. But I needed the mysql driver for the php extension since it only came with 2 (sqlLite, sqlLite2).
To add the mysql driver for pdo in your php install, put (pdo_mysql.so – you’ll have to compile this) in your extensions directory and then enable that extension in php.ini. WTF, pretty simple but there are no web pages with instructions. And compiling in Mac OS X sucks because you need to install extra Developer tools and than run the command line compile commands.