Makemusic has stated that they are dropping finale viewer in support of using NotePad as the preferred means of opening .mus files. Documents created in Finale 2004 cannot be opened in finale viewer or NotePad 2003. A new release of NotePad 2004 is expected and that will open Finale 2004 documents.
As for prohibiting downloads from your website, maybe put them in a password protected page, where you control access to who views them.
Maybe some web designers out there know otherwise, but I think if someone wants something off your site, they will find a way to get it.
"Surely you can't be serious."
"Yes I am serious...and don't call me Shirley."