Any suggestions? Timidity? I can't seem to find this on my system?
Rosegarden seems to be what I am looking for, but I can't seem to get it to play sound.
Yep if you install timidity, then you can use it as an output midi port in Rosegarden, yes soundfonts are the voicings, but timidity can do a lot of stuff, and if you're using ubuntu the default install should include the General Midi pat (patterns) sounds which it can use as well and should get you up and running. NB this is a command line prog so man timidity.
Timidity is a bit of a CPU hog but it will work on any soundcard, so Norio give it another go.