I went to remove the "Mainconcept DV codec" and was unable to remove it using ADD/REMOVE Programs. I then tried to install the newer version, as given by this site, and got an error message. WOW! I cannot install the new codec and possibly other Windows Installer software-real trouble.

I search the WEB and found this site:
http://support.microsoft.com/default.aspx?scid=kb;en-us;290301

It contains a Windows Installer CleanUp Utility. I download it and ran it, and away went my problems. It lists all programs that use the W.I. and allows you to remove the entire contents from the Registry. After removing the old Mainconcept codec, using the utility, I was able to install the new one without issue.
A good utility to have. It works for all versions of Windows 32 bit systems including Win 98.