AnyCPU/Prefer 32-bit/Class Library

Hi,

I am a little confused:

Using AnyCPU as platform target, and having a executable project (ConsolApp, or WindowsApp) I can select/deselect "Prefere 32-bit" while in a Class Library this option is disabled for changes.
- Why is that?
- If I uncheck "Prefere 32-bit" do I then get a 64-bit process automatically ?
- what happens to the "Class Libraries" in a solution, if the related executabel project is set one or the other way?

Also, in my case I need to make use of a 64-bit native C dll. I realized, that if I use "AnyCPU" and uncheck "Prefere 32-bit" I can make use of the 64-bit dll from within my "API Wrapper Class Library". Is this the right way to do it, or am I now just lucky that I can access the dll ?

Thanks for any clarification on this subject!

Regard
Rainer