Problem with pg_connect() in PHP

Dear Members of
I have installed the Apache 2.0.61,  PHP 5.2.4 and PostgreSQL 8.1 on my local computer.
All three software were successfully tested. I changed “;extension=php_pgsql.dll”  to
“extension=php_pgsql.dll”    in the php.ini file in order to enable PostgreSQL in PHP.
The problem comes when I try to connect to the PostgreSQL Database using php function pg_connect
$dbconn = pg_connect("host=".PG_HOST_NAME." port=".PG_PORT_NUM."  dbname=".PG_DB_NAME." user=".PG_USER." password=".PG_PASSWORD);
All the arguments in the function pg_connect() are defined.
Unfortunately I am getting the Fatal error: “Call to undefined function pg_connect() in C:\Web\html\Staff_Management\example1.php on line 23”
C:\Web\html is my document root.
What could be the possible mistake?
Anyone to assist me!
Best regards,
James Kitambara