You learn new stuff every day. Thanks to Brendan Smith for pointing out to me that some creative web guys have come up with a solution for running multiple versions of IE on a PC without having to run anything in a virtual machine.
Ryan Parman over at skyzyx.com has been nice enough to encapsulate all the version in nice little zip files that you can just extract to a directory and run. It doesn't appear that people have 100% success using this hack, but it seems to work for most people. The only noticable issue is that the "Help > About" will always list the current version of IE installed, but apparently the user agent reports back the expected results.
NOTE:Because this is essentially a hack, behavior may or may not be exactly what you'd get if the product was installed as intended. It appears some users were having problems w/some DHTML elements not working as expected. Just keep this in mind when using these versions of IE in testing.