Connecting to a remote postgres database

[admin]

using PHP 4.0 under Win2K IIS 5.0

got this error
-> Fatal error: Call to undefined function: pg_connect() in C:\Inetpub\PHPwwwroot\index.php on line 17

is there something i have to load...... why undefined function?

code:

$dbname = pg_connect ("host=computer.test.com port=5432 dbname=test user=user password=password");
echo ("DATABASE NAME = $dbname");
pg_close ("$dbname");


thanks in advance