On the plus side: Laptop + Ubuntu + USB MIDI interface + Casio CT-700 keyboard handed down from parents + MIDI file from music teacher + Rosegarden + Play button = music at the right pitches coming out of keyboard speakers.
Obviously it's going to take a little bit of tweaking to figure out how to make everything work exactly right...but I think I'm on the right track.
ETA: The reason for the strikethrough above...that book only addresses Mac and Windows software.
Instead, this book seems to be on the most prevalent Linux sequencing software [now does the subject line make more sense?]: