Enter Spoon.net a recent discovery which has managed to resolve this problem. Thanks to their virtualisation software I have been able to have IE6, IE7 and IE8 all running at the same time whilst all using httpWatch and AOL’s WebPageTest concurrently as well.

It’s not just browsers either, here’s a blurb from their site:
Spoon specializes in app virtualization and delivery technology, a family of sophisticated techniques that decouple apps from the underlying operating system and enable extremely rapid delivery and launch. In support of its ongoing product development efforts, Spoon conducts fundamental research in the areas of virtualization, operating systems, formal semantics, programming languages, complexity theory, and cryptography.

You’ll need to install Spoon.net’s plugin first but this is no big deal. Once installed simply click on one of the icons of the browser you want to test, if this is your first time launching that browser version it will download what I can only assume is the a local ‘image’ of that browser and when this is down will launch it just like any other application.

All in all this is an excellent site and well worth adding to your AdOps toolbox.

Downsides: Not supported on the Mac or on Chrome or on Opera from my initial tests.