As an Apple user, when I'm doing Domino development I live in VMWare Fusion to emulate Windows. And since the release of the Windows 7 Release Candidate (free until next year) doing testing in IE6 and IE7 is nigh on impossible. There are tools that you can use to emulate the different browsers (such as IETester) but I have found them to be unreliable.
It's a little know fact that Microsoft actually give out free copies of Virtual PCs setup for IE6 and IE7 compliance testing from their website. Of course because it's a virtual PC image and not a VMWare image we have to go a little further and convert the one to the other. That's where these instructions come in. You'll need to download a conversion tool, the one that worked for me was Q which is actually mentioned in the comments rather than the main body.
Once you've done the conversion, you end up with small (i.e. <1gb) Virtual Machines that you can do "proper" IE testing in until you get the nerve to tell you're idiot IE users that they need to move into the 21st century and start using one of the proper browsers.
Anyway, what it does mean is that you can leave XP and IE6 behind altogether except for your testing which can only be a good thing. Windows 7 really is a big step forwards, even for those of us who don't even like Windows.