Forgive the newb - is the expectation that I would use the Arduino I/O for the RS-232 interface (what's that you say?) which my old auditorium automation system uses. I need to have two bi-directional connections, I am essentially inserting the Tiny in-between a controller and an end device that gives status - enlighten this dullard, please - thank you. 

RS-232 uses higher voltages- you could use a RS-232 to TTL level (5V or 3.3V) adapter board, which you would need to solder to a TinyDuino prototyping board.