I run VMWare Fusion to run Windows Vista where I run IE Tester. I have to have IE 7 installed in order for IE Tester to be able to test all the versions: 5.5, 6, 7 and 8. Somedays I wish I had a real PC with a real original version of IE 6 to test on, because there are little quirks and differences between the IE Tester versions and the real thing. You could use Parallels or Bootcamp to do the same thing, and IE Tester also runs on Vista. You’ll need an Intel Mac to run either of these. If you don’t have an Intel Mac or can’t/don’t want to run Windows on your Mac, you could use ies4osx which runs on Darwine (the OS X flavor of the “wine” virtualization software that allows you to run Windows programs without running Windows). I have ies4osx kind of slow and buggy, but it’s been a while since I’ve used it.