What version of Windows are you running? If 98/ME/2000 you can go to the Control Panel and then Add/Remove programs, click on Internet Explorer (the one with out any Q on it as they are patches) and select Remove and then select the Repair option.
If XP try:
rundll32 setupwbv.dll,IE6Maintenance "C:\Program Files\Internet Explorer\Setup\SETUP.EXE" /g "C:\WINDOWS\IE Uninstall Log.Txt"