All that stuff is true, but you would really sacrifice one of those consoles instead of just dropping a cheap PC in there? The cost of a PC to run MAME for DOS *has* to be lower than the cost of a console. It seems a lot of the console's processing power would be wasting away in there. MAME does exist for the Dreamcast but it has its limitations, I suspect those limitations would disappear on the XBox, but that seems to be a long ways off...

EDIT: It seems some guy has already gotten MAME running on the XBox but hasn't released it yet. It could be fake, who knows.