PHP 5.2.5 install problems: zend_ini_string

["Joshua McGee" <joshua.mcgee@xxxxxxxxx>]

Following the instructions at http://dan.drydog.com/apache2php.html to the 
letter, I get the following error:

# /usr/local/apache/bin/apachectl start

httpd: Syntax error on line 53 of  /usr/local/apache/conf/httpd.conf: Cannot 
load /usr/local/apache/modules/libphp5.so into server: 
/usr/local/apache/modules/libphp5.so: undefined symbol: zend_ini_string

I am in RedHat Enterprise 4, with PHP 5.2.5.

Thank you.