As far as you're concerned once you've "pulled out" the contents with something like .html() it's just a string. You can test that with
<html>
<head>
<title>runthis</title>
<script type="text/javascript" language="javascript" src="jquery-1.3.2.js"></script>
<script type="text/javascript">
$(document).ready( function() {
var x = $("#foo").html();
alert( typeof(x) );
});
</script>
</head>
<body>
<div id="foo"><table><tr><td>x</td></tr></table><span>xyz</span></div>
</body>
</html>
The alert text is string. As long as you don't pass it to a parser there's no magic about it, it's a string like any other string.
There's nothing that hinders you from using .post() to send this string back to the server.
edit: Don't pass a string as the parameter data to .post() but an object, like
var data = {
id: currid,
html: div_html
};
$.post("http://...", data, ...);
jquery will handle the encoding of the parameters.
If you (for whatever reason) want to keep your string you have to encode the values with something like escape().
var data = 'id='+ escape(currid) +'&html='+ escape(div_html);