You would be better off hacking controllers.. here's why....
The xbox port of mame (not the linux port running on the xbox) doesn't have any special input drivers..... as a matter of fact i don't even think it lets you remap keys yet. Yes I know this version is technically illegal and all, but it's the only acceptable mame port you can run on xbox.
Sirp is half right on the limited power of the xbox, but the xbox specific port of mame acts like and xbox game, and thus is very optimized. It will run all games but he newer midway games (like mortal kombat, ect) at acceptable speeds. However if you run the linux port on xbox linux, then you have the added overhead of an operating system. In other words it becomes more bloated and is even slower than the dreamcast port (blaaah).
If you already have an xbox, and would like to fool around with running linux/mame on it then it sounds like a plan, but don't expect to buy an xbox and make a decent mamecab out of it just yet.
