David mentioned that you can't do a Select all.
However, when executing this script:
<?php
    $conn_string = "dbname=mydb";
    $db = pg_connect($conn_string);
    $selectfields = array("imgid" => "");
    $records = pg_select($db,"mmsfiles",$selectfields);
    print_r($records);
?>
...I get this result:
Array
(
    [0] => Array
        (
            [imgid] => 1
            [file] => /home/wietse/public_html/mms/images/1.gif
            [thumb] => 
        )
    [1] => Array
        (
            [imgid] => 2
            [file] => /home/wietse/public_html/mms/images/2.gif
            [thumb] => 
        )
    [2] => Array
        (
            [imgid] => 3
            [file] => /home/wietse/public_html/mms/images/3.gif
            [thumb] => 
        )
    [3] => Array
        (
            [imgid] => 4
            [file] => /home/wietse/public_html/mms/images/4.gif
            [thumb] => 
        )
)