for (i=0;i<document.all.tags("input").length;i++)
                {
                    if(document.all.tags("input")[i].type == "checkbox")
                    {
                        if(selected  && !document.all.tags("input")[i].checked  )
                            document.all.tags("input")[i].click();
                        else if(!selected  && document.all.tags("input")[i].checked  )
                            document.all.tags("input")[i].click();

                    }
                    }

 

 

 

<script language="javascript">
function selcheck() {
  var objs = myTable.getElementsByTagName("input");
  for(var i=0; i<objs.length; i++) {
    if(objs[i].type.toLowerCase() == "checkbox" )
      objs[i].checked = true;
  }
}
</script>