Código HTML:
<html>
<script>
function ll(chk){
if(document.getElementById(chk).checked)
{
document.getElementById("msg_1").style.display = "none";
document.getElementById("msg").innerHTML = "Activado";
}
else
{
document.getElementById("msg_1").style.display = "";
document.getElementById("msg").innerHTML = "Desactivado";
}
}
</script>
<div id="msg" ></div>
<div id="msg_1">Hola</div>
CheckBox<input type="checkbox" checked="checked" id="chk_1" onClick="ll(this.id)">
</html>