I just downloaded opensong_2.1.1-1_i386.deb and tried to install it in Debian Linux. This is a netinstall, so I may be missing something that's needed. This is the error produced by the dpkg command:
Unpacking opensong (2.1) ...
Setting up opensong (2.1) ...
/var/lib/dpkg/info/opensong.postinst: 2: /var/lib/dpkg/info/opensong.postinst: update-desktop-database: not found
% dpkg -S =update-desktop-database
So install desktop-file-utils, and you'll have the missing command.
Thanks, that did the trick.