Error: MODx requires the mysql extension when using PHP without native PDO

I was getting this error when I went to setup my modx project. After trying several suggestions I found on the message board with no luck, I finally lucked out and discovered that I had the following line commented out in my php.ini file:

extension=php_mysql.dll

Once I removed the comment on that line and restarted IIS, the setup resumed. Originally I was getting two errors, and if I remember correctly enabling this extension resolved it:

extension=php_pdo_mysql.dll

Here are the specs on my hosting environment:

Windows Server 2003 Enterprise Edition
Service Pack 2
PHP Version 5.3.2
MySQL Server 5.1

PDO is required for MODx Revolution, as well as the pdo_mysql extension.

http://docs.modxcms.com/display/revolution/Server+Requirements

Apparently the mysql extension is still being used in some tests in setup at least. These should be replaced with PDO equivalents in a future release.