i've only used the avr-pg1 with the Olimex avr-p28 board, which is a great cheap $16 substitute for an arduino, though it trades USB support for open breadboard space. you can examine the schematic of that board and compare it to the arduino to deduce the mapping.
avr-p28:
arduino:
http://www.potemkin.org/uploads/Pid/arduino_usb.jpg