Grid Check All checkbox

<script src="js/jquery-1.3.2.js"></script>
<script>

function checkall(state, formid)
{
var n = document.getElementById(formid).elements.length;
for (i=0; i<n; i++)
{

if (document.getElementById(formid).elements[i].name == "chk[]")
document.getElementById(formid).elements[i].checked = state;
}
}

function disablechk(state, formid) {

$('input[name="chk[]"]:checkbox').change(function() {
var chkLength = $('input[name="chk[]"]:checkbox').length;
var checkedLen = $('input[name="chk[]"]:checkbox:checked').length;

if (chkLength == checkedLen) {
//$('#Main').attr('checked', true);
document.getElementById(formid).Main.checked = true;
} else {
//$('#Main').attr('checked', false);
document.getElementById(formid).Main.checked = false;
}
});

}
</script>


<form name="FrmName" id="FrmName" method="post">
<input type="checkbox" name="Main" onclick="javascript:checkall(this.checked,'FrmName');" />
<input name="chk[]" type="checkbox" onclick="javascript:disablechk(this.checked,'FrmName');" />
<input name="chk[]" type="checkbox" onclick="javascript:disablechk(this.checked,'FrmName');" />
</form>