TopThe top answer didn't do it for me, this. This did though:
<script type="text/javascript">
$(document).ready(function(){
$("#li_13").click(function(){
if($("#agree").attr('checked')){
$("#saveForm").fadeIn();
}
}
else
{
$("#saveForm").fadeOut();
}
});
});
</script>
UPDATE 20121213: Basically when the element #li_13 is clicked, it checks if the element #agree# agree (which is the checkbox) is checked by using the .attr('checked').attr('checked')
function, if. If it is then fadeIn the #saveForm element, and if not fadeOut the saveForm element.