handling .mus files on Musescore

As I have discovered on this forum and through trial and error, Musescore cannot handle .mus files (as from FINALE)..
Three questions:
1) What kind of files does Musescore create?
2) Is there a free program available which can convert .mus files to those which can be used by Musescore?
3) Does anyone know of a non-proprietary Linux based application which can create and display ,mus files?

Reasons for asking:
My computer has a 320 Gig Hard drive which has both a Windows XP partition and a Ubuntu Partition. As Windows operating systems are becoming more complex and more expensive, I'd like to become familiar with the Linux OS's which currently appear to have some big advantages over Windows OS's. . Rhythmbox (the Ubuntu Jukebox) seems to be comparable to J Rivers Media Jukebox 8 in handling music files, playlists, etc. Other programs like Open Office are also non-proprietary and free and can replace the similar Microsoft applications.. Musescore appears to be a program which can adequately replace FINALE excepting the importing of .mus files.

Thanks,
tlcmd