Recently I had a requirment to run multiple versions of IE for testing , after investigating I came accross this link and found it very helpful.
http://www.skyzyx.com/archives/000094.php
Zipped versions of IE are available from this site and they run parallel to IE original install, the only issue is that cookies are not set by these versions, so you need to access a site first in regular main IE and then copy over the URL to previous version of IE like 5.5 and 5.01.