I recently ran into a situation where there were two versions of PHP on a server and I needed to make sure PHP 5 was being used. To pick the version – all you need to do is add the following into your .htaccess file (assuming you do not have access to your httpd config):
For PHP 5:
AddType application/x-httpd-php5 .php
For PHP 4:
AddType application/x-httpd-php4 .php
It does not get much more easier than that!