function addOption( listBoxRef, optVal, optName )
{
    var newOpt = document.createElement( "OPTION" );
    newOpt.value = optVal;
    newOpt.text  = optName;
    listBoxRef.options.add( newOpt );
}

function clearListBox( listBoxRef )
{
    while ( listBoxRef.options.length > 0 )
    {
        listBoxRef.options.remove( 0 );
    }
}