pg_connect error

Hello, I have this problem with a connection to postgres server (running in a win2000 server).
When I connect with pgAdmin to the same postgres server works ok, but when I try to connect from php5 the connection fails.
Can help me?
Thanks.

$db_conn = pg_connect("host=SQLMACHINE port=5432 password=xxxx user=postgres dbname=compraventa1");
if (!$db_conn): ?>
    <H1>Failed connecting to postgres database <? echo "compraventa1" ?></H1> <?
    exit;
endif;


Ovax