The HowTo Forge website has a new tutorial CentOS users out there might want to check out. It steps through the installation of a MSSQL database extension for PHP (it's not installed by default) from the yum repository.
As you might have noticed on Centos 5.0, there is no PHP-MSSQL module/extension available in the default yum repositories. So if you want to use it you can alter the PHP binary or you can compile an mssql module/extension. In this article I will explain how to compile the mssql module/extension.
It's a pretty simple process involving only a few downloads (RPM files) and altering the contents of some configuration files to make things work together happily. In the end, you'll have a dynamic extension you can load into your PHP installation whenever you want.