Windows 7 includes Windows Internet Explorer 8: if you've installed Windows Internet Explorer 9, go to Control Panel -> Programs -> Programs and Features -> Installed Updates, select "Windows Internet Explorer 9" from the list and click "Uninstall";
then reboot your system and use Windows Internet Explorer 8 compatibility view feature (http://support.microsoft.com/kb/969360/en-gb).
If you really need to use a browser version older than IE8, rely on virtualization by using Windows Virtual PC with XP Mode (http://www.microsoft.com/windows/virtual-pc/) and installing
Windows Internet Explorer 7 (http://www.microsoft.com/download/en/details.aspx?id=2) within.
Bye.
Luigi Bruno - Microsoft Community Contributor 2011 Award