Well, this might be obvious...
... but if you only want to use .php4/3 files and NOT to use old version of PHP interpreter, just add handlers for them to /etc/httpd/conf.d/php.conf:
Code:
#
# Cause the PHP interpreter to handle files with a .php extension.
#
AddHandler php5-script .php
AddHandler php5-script .php4
AddHandler php5-script .php3
AddType text/html .php
AddType text/html .php4
AddType text/html .php3
Cheap trick, but this might save you from some headaches... especially with old phpMyAdmin and php3-files when you absolutely have to use them. ;-)