PHP Login Sessions

What am I doing wrong here? I have a login form that visitors enter their "use"name and "use_psswrd" in to log in...the form action is this code: ========<SNIP 1>========== <? session_start(); if ($_REQUEST[use_name] && $_REQUEST[use_psswrd]) {

        $connection = mysql_connect("SERVER","USER","PASS") or die ("Couldn't make connection.");
        $db = mysql_select_db("DB", $connection) or die ("Couldn't select the database.");
        $sql = "select * from TABLE where use_name = '$_REQUEST[use_name]' and use_psswrd = '$_REQUEST[use_psswrd]'";
        $sql_result = mysql_query($sql) or die ("Couldn't execute query.");

        if (mysql_num_rows($sql_result) >0 )
        {
                list($valid_id, $valid_user) = mysql_fetch_row($sql_result);
                session_register("valid_id", "valid_user");
                // echo "$valid_id, $valid_user";
                header("Location: modify_profile.php?uid=$valid_id&un=$valid_user");
        }
        else
        {
        header("Location: profile_login.php");
        exit;
        }

} mysql_free_result($sql_result); mysql_close($connection); ?> ======<END SNIP 1>======= That page is supposed to register a session that holds both the "valid_id" and "valid_user" variables and continue on the the next page (which it does) - BUT once the user gets to the next page: =======<SNIP 2>======== <? session_start(); if (isset("valid_id")) {

        echo "$_SESSION[valid_id]<P>";

} else {

        echo "DUMBASS!";

} ?> ======<END SNIP 2>======= Nothing gets displayed.....Am I not setting or requesting them correctly?? The one thing I cant understand is why the URI now reflects the user is logged in: (modify_profile.php?uid=1&un=jerry) TIA, Jay