Ok, new problem...
My shiny brand new X-Arcade Tankstick seems to be working fine in the OS (10.5.5) (every key is responding, registered in system profiler)
But as soon as I launch SDLMAME (0.128u1), it just hang there, eating 100% of one processor core.
Force quit has no effect.
Nothing to do except restarting the MacPro.
Same result if I launch from MameTunes.
Can't post the crashing report: too big...