Controllare un array di checkbox

[fcaldera]

<form ... onsubmit="return atLeastOneChecked(this)">
...
</form>

function atLeastOneChecked(form) {

   var inputs = form.getElementsByTagName('input');
   var i = inputs.length;
   while (i--) {
      if (inputs[i].checked) return true;
   }
   return false;

}