Usually, the best way to see if you can repair a program without performing a clean reinstallation is to check in your Control Panel, for the option to Uninstall a Program (in Vista) or Add or Remove Programs (in XP). From there, by choosing to uninstall the program, it would sometimes give you the option to repair it instead. Unfortunately, since Internet Explorer is pretty much glued to Windows, you can’t really uninstall it. As a result, the option isn’t there, so we'll just have to find another way.
Of course, for XP users, you can remove your upgraded version of Internet Explorer, but that would just revert to version 6, which doesn’t really help.