not seeing postgres function in php/apache (newbie)

I'm setting up a system (for development) and get the following error:

Fatal error: Call to undefined function: pg_connect() in
/var/www/htdocs/test_pg.php on line 3

PHP 4.3.4 was configured with this:
./configure --with-pgsql --with-apxs --with-mysql --with-pear
AFAIK no errors in ./configure ---> make install steps.

I would like suggestions on the things to check, or procedures to help
debug this. I'm not very experienced with Linux, Apache, PHP, or
Postgres. I just setup this system so any of the four components above
could be faulty. I went through php.ini and httpd.conf per the install
guide in the php source.

Apache serves up it's default start page, phpinfo() works, and I can
create a db with psql.

The distribution is Slackware 9.1.

Thanks in advance.