The ‘PROGRAM’ header is used to upload the code onto the UPOD. It is nothing more than a pinout of the Serial Rx/Tx pins, ground and the atmega reset pin.
There are several USB-to-serial modules available that can be used as a programmer, such as the FTDI basic or the FT232 breakout board, both available from Sparkfun. Check out this tutorial if you decide to go this route (note: connect the DTR pin to RESET on the UPOD if you want the Arduino IDE to automatically upload the code).
The most transparent method to program the UPOD is using an Arduino Uno itself. Remove the Atmega chip from the Arduino, and connect it to the UPOD as below. Now the Arduino IDE thinks the UPOD is an Arduino. If you will be programming many UPODs, it may be advantageous to build yourself a ‘programmer’ with a chip-less Arduino Uno and the male receptacle for the program header.