The biggest problem you have as a webdeveloper is that you have to check everything in like a thousand different browsers. But the biggest few will do. Internet explorer is one of the most important ones since it is still the biggest and most used. And it comes in three flavors. The good (IE8), the reasonable (IE7) and your worst nightmare (IE6). Win 7 makes it real easy to run all three on the same machine.
I would suggest reading the article “Run IE6, IE7, and IE8 on the Same Machine Using Windows 7 XP Mode” by Craig Buckler.
It is pretty easy, even I got it to work from the first time.
See the result.
and you don’t even see them running in the Virtual machine. Not that this will make your life much eassier if you want IE6 compatibility but at least it will make it a bit faster. And you will be sure you have the correct engine and not some emulation.
There are lots more you can do with XPMode in Win7.