Hi Miso !

My understanding of your problem is that you wanna move a class from one .vcx class library into another library. Here is how you can solve that during the design mode (you didn't ask for programatical way to do that).
In MSDN Library Visual Studio 6.0 find the keyword sequence: class definitions > modifying > "Copying and Removing Class Library Classes" header.
You can figure out that you should copy a class into a new library and after that remove the same class from the old library.