It is just not possible to run php4 as php5 is installed as default.
This is assumption not correct. I recently installed it for a customer: php as mod_php + php4 as cgi.
1) Install the php4-cgi package from your linux distribution.
2) To enable PHP4 in a website, add these two lines in the
apache directives field of the website:
Action php4-cgi /cgi-bin/php
AddHandler php4-cgi .php
And then make sure that the following options are disabled: