Also, you may find this site useful, which allows you to test using all versions of IE over the net (using screenshots). I've found it handy and accurate. http://ipinfo.info/netrenderer/index.php
What version of Windows are you using? If you're using XP, you can download a standalone version of IE7 here. I think the blog also has versions of IE6 as well.
Basically googling IE6 IE7 standalone will help too.