Originally Posted by Hans
Is it possible to add this as a little extra to a server running Debian 3.1 according "the perfect setup" including ISPConfig?
Yes, but I'd then put
AddHandler php-script .php4
Action php-script /cgi-bin/php4
into each Vhost seperately (using the Apache Directives field of ISPConfig) because otherwise PHP4 is always on (for every web site).
Also check the PHP5 configuration: PHP5 should not be enabled globally, so you must change /etc/apache2/mods_available/php5.conf (otherwise PHP5 is enabled for every web site, no matter what you specify in ISPConfig).