$dbobject =& singleton::getInstance('other_table');
$dbobject->sql_select = 'other_field';
$other_data = $dbobject->getData("other_id='whatever'");

    function _cm_initialiseFilePicker ()
    // perform any initialisation before displaying the File Picker screen.
    {

        $sv = $GLOBALS['HTTP_SESSION_VARS'];
        $svp = $sv['pages'];
        $keys = array_keys($svp);
        //get previous page in stack ... you may need to adjust the 2
        $page = $keys[count($keys) - 2];
        $task = $svp[$page]['task_id'];
        $where = $svp[$page][$task]['where'];

        //the field we want
        $field = 'your_table_pkey_id';

        //Tony's sample code (more or less)
        $dbobject =& singleton::getInstance('your_table');
        $dbobject->sql_select = $field;
        $data = $dbobject->getData($where);

        $primary_key = $data[0][$field];

        // now do something with the primary key
        //.....