Question: How toturn .h file +dll into some kind of .Net wrapper? or something like that? (no C\C++ sources just h files)

Answer: 
If you look at the documentation for [QDesktopServices::openUrl()](http://doc.trolltech.com/4.6/qdesktopservices.html#openUrl) you will see that:

> 
> If a mailto URL is specified, the
>  user's e-mail client will be used to
>  open a composer window containing the
>  options specified in the URL, similar
>  to the way mailto links are handled by
>  a Web browser.
> 
> 
> 

So using [QDesktopServices::openUrl()](http://doc.trolltech.com/4.6/qdesktopservices.html#openUrl) you should be able to open both the *default navigator* and *default mail client*.

I assume you want to open these applications and not just find out what they are.
According to Microsoft you should not use the registry directly.
See : <http://msdn.microsoft.com/en-us/library/windows/desktop/cc144154(v=vs.85).aspx>