I actually have a GP2X... it's a handy little gadget to have. Never looked into it for music notation, but it is fun and functional nonetheless... I think you should look into a program called LMMS. It is a linux clone of frooty loops (for windows) and it is pretty extensive. On an N800 that boots from SD, it shouldn't be too much of a pain to install... I'm sure the port will be a little heavy, no matter what you do... but it would be a great program to use on a portable touch screen device