In this recent post to his blog Stefan Koopmanschap shares some of the troubles (and a solution) when he was dealing with getting the Geoip PECL extension installed on his Zend Server setup in OSX.
Today I needed to get a client application up and running on my local system. This application uses the Geoip PECL package, so I needed to get this up and running. This turned out to be slightly more difficult than just a PECL install, as you're missing some libraries by default, so here is my log of things to do to get it up and running.
He gives the complete list of steps his followed including downloading the source and his way around this "System could not load this extension" issue. The trick was to recompile the source with the correct architecture. By default his extension was built with i386 instead of 64-bit but updating some of the CFLAGS settings (and a few other environment variables) got things compiling correctly.