I recently got nano-X running on the gumstix, but now I need a way to control the interface.  I have a custom-made daughterboard with a directional pad wired up to GPIO, but I'm not sure how  to trigger an event when a button is pushed.  Can anyone give me some pointers on accessing the GPIO information, or for example triggering a program to run when a button is pushed?  I eventually want to be able to navigate thru a web-interface with this directional pad.  Thank you.