At work we have various web based applications that will only work on Windows and IE, a situation I consider to be a contradiction and maddening. (Look! We're web based! Er, actually we're not because we install all sorts of windows specific crap, but we get away with giving you a crappy user interface because that's what you expect on the web. Robert is right.) Fortunately, VNC comes to the rescue. The best VNC client for OSX that I've found is VNCViewer. This page also has links to other VNC clients for OSX.