chaynic,
<script>
function func() {
if (document.getElementById("name").checked) {
document.getElementById("lastname").disabled = true;
document.getElementById("lastname").checked = false;
}
else {
document.getElementById("lastname").disabled = false;
}
}
</script>
<input type="checkbox" id="name" onClick = "func()">1
<input type="checkbox" id="lastname">2