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.
On Windows this kind of stuff can be recovered directly from the registry (regedit).

Search the web to find out the specific registry paths, like [this](http://www.ehow.com/how_6325458_configure-browser-using-regedit-xp.html).