By your example alone, you're missing a reference to the required files, and you're not wrapping your jQuery code in script tags. You need to reference not only jquery-source, but jquery-json, and jquery-session as well.
<script type="text/javascript" src="scripts/jquery.js"></script>
<script type="text/javascript" src="scripts/jquery.json.js"></script>
<script type="text/javascript" src="scripts/jquery.session.js"></script>
Once you've got those in place, you need to place your logic within script tags:
<script type="text/javascript">
$(function(){
$.session("foo", "bar");
});
</script>
See the following demo for an example: http://www.jaysalvat.com/session/test1.html
Lastly, the language
attribute of the script
tag is deprecated. You can do away with it, but keep the type
attribute.