designing Modules with C++

Hi to All

Could anyone please give me some links or docs or any hints for the following

I am trying to learn to design a project. Say I have 5 modules...I want to interact each module from every module by means of messages(class objects)....
Till now I was planning to make all the 4 modules as a dll and get the methods dynamically from the main modules...But thats just an imagination, and this may not be efficient too. I have not implemented anything yet....Could anyone give me some tips or hints to do the same.

Also if there is any other methodology to do so...

Basically I am trying to design a project with several modules...Its just for my self learning...

thanks in advance

-----------------------------
I am a beginner