Would love to have lilypond on N900 -- but building it from source on the device proved to be beyond my skill as well. Even when it did build with the correct confluence of guile, tex, and lilypond source versions, the PDF output was erraneous.

Just because it builds doesn't mean it works. But best of luck! And if all else fails you can always write Lilypond files in a text editor and live headless until you get to your workstation