<Script Language="JavaScript">
 function chkall() {
  if (pm.delall.checked == true) {
   for (var i=0; i<pm.elements.length; i++) {
    pm.elements.checked = true
   }
  }
  else {
   for (var i=0; i<pm.elements.length; i++) {
    pm.elements.checked = false
   }
  }
 }
</Script>

<form name="pm">
 <input type="checkbox" name="delall" value="" onclick="chkall()">
 <input type="checkbox" name="delpm" value="1">
 <input type="checkbox" name="delpm" value="2">
 <input type="checkbox" name="delpm" value="3">
 <input type="checkbox" name="delpm" value="4">
 <input type="checkbox" name="delpm" value="5">
</form>