I'm sure this thread is long dead, but for anyone who has this problem in the future, the answer is to change the User-Agent header sent by the browser (as long as there are no javascript checkers). This guide is related to IE8, but I'm sure it will point you in the right direction.
The other solution would be to have a bunch of Virtual PC machines running, each with different versions of IE installed - but it seems a bit extreme just for testing compatibility.