The best way to run ie7 - ie10 on a mac that I found is to run oracle virtual machine and install all versions of the browswer. This route is completely free and runs outside the browser like some of these other options.
The only downside to this method is it takes up a lot of space.
Here is the easy to follow tutorial:
http://osxdaily.com/2011/09/04/internet-explorer-for-mac-ie7-ie8-ie-9-free/
