If you go to Start>Settings>Control Panel>Add/Remove Programs and then select Microsoft Internet Explorer, click Add/Remove there is an option in there to repair it.
Try this first.
Uninstalling any version of IE is dependant on your operating system, some versions ie Windows 2000 will need re-installing afterwards as uninstalling IE will also remove some components for the windows.
You will also lose Outlook and Outlook Express files as well in other systems.
If you go to: Crogram FilesInternet Explorer and check the read-me file, you will find further information there.