On the DotKernel.com site today there's a post walking you through the installation of the GeoIP extension on Zend Server (5.6) on Windows. It starts with a bit of test code to check and see if you might already have it installed.

The steps are relatively easy:

• Download the extension package
• Copy it to the right location
• Use the Zend Server interface to turn on the extension
• Download and copy some geoIP databases from Maxmind

Most of these steps go for any extension you want to install, but keep in mind since it's Windows you'll need the .dll file, not the source to compile. Some extensions may not have this available for download.