The Bootloader is a .hex file. Once this .hex file has been "burnt" to the chip you can transfer sketches to the Arduino's ATMega via its serial pins. For this task you would then need a serial-to-TTL-converter, as the ATMegas logical TTL-levels are different from the ones of the RS-232-protocol the computers serial port uses.
yo there Otacon,
i have a USB to RS232 cable.
i just load the bootloader (hex file) into the Atmega168, and
after that, i can just use this USB to RS232 cable to program?