I wouldn't uninstall anything. Just go through your httpd.conf file and comment out all of the PHP related directives.
Here is what should be in there.
LoadModule php4_module modules/libphp4.so
AddModule mod_php4.c
AddType application/x-httpd-php .php .php3 .phtml
AddType application/x-httpd-php-source .phps
For starters try and configure PHP with the following command.
./configure --with-apxs --with-mysql
For this to work you will need the apache-devel and the mysql-devel packages installed.
After you run configure for PHP, run the following commands to install it.
make
make install
This should modify the httpd.conf file for you. The only line you want to check will be the LoadModule line to make sure that it points to the actual location of libphp4.so. Hopefully this will help you a bit.