As a designer and developer of websites I've had the same problem that everyone else had, trying to test my websites in IE6 as well as the standard Vista install of IE7, and more recently I've had to test in IE8 beta too. That on top of Safari, Netscape, Opera, good old Firefox and now Chrome. Headache!

As anyone with Vista knows, IE6 just won't run on the OS, it's like getting me to swim more than one length; reasonably impossible. The old solution back in XP days was to use the powerhouse that was http://tredosoft.com/Multiple_IE but again, Vista kicks it out and doesn't like it.

So, the options?  Well you can always reinstall XP, but personally (get ready, I'll get a right pasting for this) I actually like Vista. I'm runing a machine wealthy of resource so I hear what people say about it being slow on some machines but if you have the power then use it I say. You never saw Lion-o having a word with Tigra along the lines of "nah, today I'll not use the sword, I'll just do it with the old fisticuffs" did you? Put those tools to work I say, here here.

So anyway, back to the options.

For a good while I was using the greatly received Microsoft Virtual PC solution which did work well, but it was awkward to set it up to receive a local connection (for testing from your local IIS or whatever development server you use) and it was a sap on the old pc resources. Still if you want to try it:

Microsoft Virtual PC download: http://www.microsoft.com/windows/downloads/virtualpc/default.mspx

Virtual Hard Drives (including IE6, 7 and 8): http://www.microsoft.com/downloads/details.aspx?familyid=21eabb90-958f-4b64-b5f1-73d0a413c8ef&displaylang=en

How to network it up: http://pingv.com/blog/glhines/200712/browser-testing-ie6  

So, I figured that option was workable but not ideal and I refuse to buy another machine to do the IE6 testing on.  Whilst I was digging around I found a nifty little solution for testing multiple IE versions in a browser (http://ipinfo.info/netrenderer/) but it only serves up results from an online webpage, not a local host.

Finally after surfing around for a good while I found and installed this: http://www.my-debugbar.com/wiki/IETester/HomePage which appears to have solved all my problems!

IETester lets you open up several tabs within one browser window with each tab representing any IE browser from IE5.5 right up to IE8 Beta 2, and to be fair it does seem to faithfully represent the way each browser natively renders any given webpage and it's CSS.  I'd even go so far as to say it works with Javascript fairly well too based on that fact that this here blog site of mine uses jQuery and jQuery corners for the rounded divs and it renders fine in all except IE5.5, which is to be expected.

So, this is easily the best solution that I've found after my time consuming searching and I'd urge anyone that needs to test multiple versions of IE under a Vista OS to give it a shot.