I have recently been playing with Milkytracker on the GP2X, which only has a 200Mhz ARM processor and a 320x240 screen but is still capable of running Milkytracker very well (if you don't mind using the joypad instead of a mouse). Milkytracker is a lot more powerful, stable and feature complete than any other tracker for Linux except maybe skale tracker but that hasn't been updated in years, is not FOSS, skale is only available for Windows and x86 Linux and nor does skale have a 320x240 mode as far as I'm aware.
Milkytracker is not yet open source but the author does plan to open it when he's happy with the state of the code. There is a ARM Linux binary of Milktracker available for download already that is supposed to work with the Zaurus but it didn't work on my c3000 under cacko so maybe its a pdaXrom bin? Could somebody try it under pdaX and let me know if it works? Anyone interested in porting Milkytracker or making changes to the code can get in touch with the author