http://www.my-debugbar.com/wiki/IETester/HomePage

IETester is a freeware app that lets you view web content in several versions of IE. In the past you could only have 1 version of IE loaded on a windows machine at a time. This made many people wait to update their IE so they could still test web pages in the older version. With IETester feel free to upgrade to the latest IE.

I have been checking out how well it emulates the different versions of IE and so far it does a pretty good job. The CSS and JavaScript support is pretty spot on. If you need to develop sites then download IETester.