You can install IE6 and IE7 on the same PC using "Virtual PC" software.
http://www.microsoft.com/windows/virtualpc/default.mspx
It's beyond my capabilities so don't attempt it unless you know what you are doing. IE6 and IE7 form part of the core operating system program so you can't mix them. A virtual PC means that it effectively creates another operating system.
Other browsers are just programs like any other so you can have Firefox, Opera or others on the same drive as IE and open in different windows.
IE7 requires OS XP
http://www.microsoft.com/windows/ie/...s/default.mspx
To get an earlier version of IE you would probably have to get an earlier operating system or uninstall a previous upgrade but I would not recommend going backwards.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.