<script>
function selectALL() {
var formELS = MyForm.elements;

for(var i = 0; i<formELS.length; i++) {
if(formELS[i].type == "checkbox") {
formELS[i].checked = formELS["checkmadre"].checked;
}
}

}
</script>

<input type="checkbox" name="checkmadre" onclick="selectAll()">