function doStripe() {
  tbodies = $$('tbody');
  for (var i = 0; i < tbodies.length; i++) {
    var found = false;
    var classes = tbodies[i].parentNode.className.split(/ +/);
    for (x = 0; x < classes.length; x++) {
      if (classes[x] == 'nostripe') found = true;
    }
    if (!found) {
      var odd = true;
      for (var tr = tbodies[i].firstChild; tr != null; tr = tr.nextSibling) {
        if (tr.nodeType == 1 && tr.nodeName == 'TR') {
          tr.className = (odd) ? 'odd' : 'even';
          odd = !odd;
        }
      }
    }
  }
}

Event.observe(window, 'load', doStripe);