There is technically a way of running IE6 and IE7 side-by-side, but it's not supported by Microsoft and involves editing your registry, downloading files from third-parties, losing some functionality, and potentially putting your computer's security at greater risk. Thus, it's not recommended.

Instead, try the User Agent String Utility, which makes IE7 report itself as being IE6...it is a temporary solution for some compatibility issues. Otherwise you can uninstall "Windows Internet Explorer 7" through Add/Remove Programs, which will automatically restore IE6.

Hope this helps,
John