Can't Get PHP Going on PostgreSQL

I am new to both PHP and PostgreSQL. Trying to install PHP and PostgreSQL 8.0 on Slackware Linux 10.0.0 .
I am getting the following error out of Apache:
"Fatal Error: Call to undefined function: pg_connect() ...."

PostgreSQL is up and running, and appears to be fine.

Have found a lot of web references to this; the best was http://us2.php.net/pgsql . But am unable
to proceed because I am not sure what to do.

Facts about what I have installed:
- Installed PHP from Slackware binary; I made no special efforts to compile it. According to a PHP utility
function (phpinfo()), looks like it might be configured for MySQL already.
- version info:
PHP = 4.3.7
Linux kernel = 2.4.26
Apache = 1.3.31

How do I find these functions and install OR configure the php.ini file?

I don't think this is hard to fix, but it is beating me up right now. What I need to find a blow-by-blow of
what to do. Can somebody help me?