function invertSelections(form)
{
  var len;

  if (!document.forms[form].elements['items[]']) {
    return;
  }

  len = document.forms[form].elements['items[]'].length;

  if ( len ) {
    for ( i=0; i<document.forms[form].elements['items[]'].length; i++)
      document.forms[form].elements['items[]'][i].checked = !document.forms[form].elements['items[]'][i].checked;
  } else {
      document.forms[form].elements['items[]'].checked = !document.forms[form].elements['items[]'].checked;
  }

}