I'm doing web development on a Windows 8 system. I'm running the latest IE, but I need to test the app with older versions of IE as well (especially IE7 and IE8).
Is it possible to run these legacy versions of IE on Windows 8?
You use virtual machines to do this, it is the easiest way. You use Hyper V and the VHD images provided by microsoft (or use a third party tool like virtual box).
First off, setup Hyper V as per the instructions given by Kronos here.
You can then download the respective vhd images from Microsoft and create a virtual machine for each version of IE.
Open the Hyper V manager and create a new virtual machine.
Enter the name, memory details etc, but then for the hard disk image, select use existing hard disk.
Click finish and you will have your VM that has the legacy versions of IE.
HowToGeek has a large tutorial of getting the individual VM's running here.
If you need a stand-alone testing tool you can try BrowseEmAll. It runs IE 7, 8, 9 and 10 alongside.
For simple testing purposes I find IETester works pretty well.
You might be able to work around the problem with the Developer Tools. Open IE (desktop mode) and press F12 (or go to Tools > Developer Tools).
In the toolbar, you can select the Browser Mode and the Document Mode. There's an extensive explanation on how it works and what the difference is between these two mode.
You can use this site to test browser compatibility: http://browsershots.org/
What's wrong with just pressing F12 in IE9 and set compatibility mode to IE7/IE8 ? I have never noticed any differences between the real browser and IE9's built in browser simulator.
VMWare Thin App, might be something you want to look at for not just the browser but any app that must be run in an environment that the host OS cannot support.