Note for Arduino 1.0: you need to make one small change to the ArduinoISP code. Find the line in the heartbeat() function that says "delay(40);" and change it to "delay(20);"
The serial signals that you get from an actual rs232 port are inverted and at higher voltage levels than the signals you'd get from an FTDI breakout board or similar. It won't work, and it might fry your chip.
Isnt that why the RS232 interface is there (given in the schematic).