I've a credit card applicatoin along with a dll, both designed in Delphi 2006.

I've an class that comes from basics class and overrides several virtual techniques.

The course is passed towards the DLL with an released method, the released method only is aware of the bottom class. I call the techniques around the class from inside the DLL the overridden techniques aren't invoked.

Can there be something I have to do in order to get this work? it's it really difficult?

You cannot create an item in a single module and call its techniques inside a different module. By module I am talking about .exe/.dll.

If you want to mix limitations such as this, then you should utilize packages, COM reely functions. Packages look alluring but bind you into utilizing the same compiler for those packages within the system. If that's not limited for you then proceed and employ packages. Otherwise use COM reely functions.