When trying ez publish 3.6(.3) with PHP 5.1.2, you will see the following message:

Unsupported PHP version 5.1.2-1

You cannot use this PHP version with eZ publish 3.6.3.
You will need to upgrade to eZ publish version 3.7 or higher.

Obviously, upgrading to eZ publish 3.7 wouldn't help either. We'll have to change the message.