In need of advice to hiding forms and classes

Hi Everyone,
I need help with the following project:

The project was originally in vb6 and I have converted it into vb.net 2008, it has many classes(modules) and forms, and the client wants to sell it, so others can make something out of it. However they only want others (buyers) to see one class and everything else hidden. He wants to sell the source code only to one class which is the main one, and does not want them to see the forms and other classes.

Buyers can modify and make the source their own to a certain extend, by only modifying one class.

I was thinking if I create another project and add all the other classes and forms in it, build it, which it then creates a dll file, and then reference that dll file into the main project leaving everything else hidden from the buyer.

I am not an expert in programming my knowledge is limited, this may not be the best idea of doing it, however if anyone else has a better idea I'm willing to listen and give it a try.

Please help
Thanks in advance
AT