As I worked to convert the c# info in my post about saving a web page as an mht file, I ran into a problem with the reference to cdosys.dll.
A little research brought me to this page:
318823 - CDO for Windows 2000 Library Reference Is Unavailable in Visual Basic Project
There I learned:
If you try to create or modify a project that references the Microsoft Collaboration Data Objects for Windows 2000 (CDOSYS) Library, the reference is not available. The reference for the Microsoft Collaboration Data Objects (CDO) for Exchange 2000 Library is present instead.
So the quest continues.
I have ran into this also and here is what I did. You unregister the cdo.dll that is currently on the 2000 or xp machine and register the older cdo 1.1 in my case. Then open the project and everything was fine.