Its not clear what variable your wanting to pass, but using load(), the simplest way is probably just to attach it to the url....
<script>
$(document).ready(function() {
$('a', $('td')).click(function() {
$('#content').load('mods/' + $(this).attr('id') + '.php?id='$(this).attr('title'));
});
});
</script>
You could also use the second argument, though it doesn't really matter, both ways will use GET and your data will show up within the $_GET array.
I'm sure I've said it before but you really should take a good look at the jQuery manual. http://api.jquery.com/load