If you're testing locally you need to use the http: prefix for the external hosted jQuery script. And there appear to be some invisible non-standard characters in the code, at least as pasted into your above post. Try:
Code:
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Untitled Document</title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8/jquery.min.js"></script>
</head>
<body>
<select name="division-select" id="division-select">
<option value="halter">Halter</option>
<option value="english">English</option>
</select>
<div>
<p class="halter">halter class 1</p>
<p class="halter">halter class 2</p>
<p class="english">english class 1</p>
<p class="english">english class 2</p>
</div>
<script>
$("#division-select").bind("change", function() {
$("." + this.value).show();
$("p:not(." + this.value + ")").hide();
});
</script>
</body>
</html>
Additionally, no need to 'not' if you change the order:
Code:
<script>
$("#division-select").bind("change", function() {
$("p").hide();
$("." + this.value).show();
});
</script>
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