Program Atmega328 with bootloader already loaded

you are right.. let me ask it this way:

I have an arduino 2009 board with atmega328, and an atmega328 which is in a working circuit (not a board, it has no usb, serial or ICSP connections) and has the arduino bootloader preloaded in it.

What is the simplest way to program the in circuit microcontroller through the arduino 2009 board?

thanks