When ever a client requires that the application you are going to build for them must be backwards compatible, their old browser become you’re new problem.  Fortunately, if the old browser is Internet Explorer, you now have hope!  Thanks to a link forwarded to me by my friend Mark Schmidt, there are several ‘stand-alone’ versions of Internet Explorer available for download that can be run along with your currently installed version of IE.  Visit Evolt.org to download everything from IE 3 to IE 6.