PlayStation Portable coder ethan, who developed a complete synthesis/sequencer
system for PSP console (http://dspmusic.org/psp/) (yes, a synthesis system
on the PSP :-) ) has released a beta version of his sequencer PSPSeq 2.10 for Windows here:

http://www.dspmusic.org/psp/PSPSeq210ForWindows-beta1.zip
(announce here: http://groups.google.com/group/pspseq/browse_thread/thread/2b6f0912d013b190)

Not the easiest control system in the world but fun/interesting enough to give it a try.
No source code, sorry...

Moreover http://dspmusic.org/ has lot of interesting info for pepole interested in
audio implementation on dsp..

Cheers,

AlbertoZ