Copy and paste this it works now.
Couple of things you'll need to do - in the window.location i've redirected it to hotmail you'll have to change it to being the page you want to display. Also at the moment only option 2 will redirect the user in the function 'funcNewURL()' you'll need to include the addresses for the other options in the function.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<script language="javascript">
function funcNewURL()
{
if(document.form1.DropDownList.options[2].selected == true)
{
window.location="
}
}
</script>
</head>
<body>
<form method="post" name="form1">
<select name="DropDownList" onChange="funcNewURL();">
<option>Please Select...</option>
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
<option value='4'>4</option>
<option value='5'>5</option>
</select>
</form>
</body>
</html>