How to use Php connecting to pgsql

Dear All:
    I come across a problem that I can't solve it, Can anyone help me, Thanks.
    My configuration is RedHat AS4 + php5.0 + pgsql 8.1. When I finish install php, I install php_pgsql module in order
touse php connecting pgsql.  To my surprised , I can't get access to pgslq, there's nothing show on the page. 
    So I write <?php phpinfo() ?> it works.
    I write <?php echo "hello world" ? $db = pg_connect(dbname=foo, user=foo,password=foo); if(!$db) print("error")?> ,
itdoesn't work , only print "hello world" on the page. 
    But I use psql command with the same username and the same password, I can access to the pgsql.
    Does anybody know how to solve it? Thanks
MARK