Re: icons
It must be possible somehow - I have seen different icons for XML files - they even open different applications. All you need to do is find out how - and I'm sure it involves a) fiddling with the registry, and b) Knowing technical differences between the two file formats (and since they're compressed, it might be awkward).
Normally, in windows, a document file is given the icon of the application that opens it. This is dictated by the file association in the registry and is a function of the filename's extension.
If however, you create a "shortcut" to the document file then the option to change the icon becomes available...