Strong Hints On Flashing Your Xbox
customsex writes: "bunnie has written a nice one with pictures documenting his adventure flashing his bios on his xbox. check it." His page also points you to the Sony vs. Connectix case regarding reverse engineering of hardware.
Even if you can't read the bios flash part it is important in understanding how the device starts up. Chances are that if you can get your own executable onto the box you should be able to do whatever you choose and install some sort of interface that will allow for continued hacking/exploring. Knowing whats in the bios might also allow for changing the harddrive out, or having the ability to use the other 64MB ram footprint on the pcb.