The AVRISPmkII is a great device for programming microcontrollers. However, there is one drawback - the target board needs to provide its own power supply. This can be a hassle, especially when the programmer itself is drawing power from through the USB cable. Here is an easy way to break out the 5V USB power line.
Step 1: Disassembly
The mkII has a simple snap-together case. Pry back the four tabs on the underside with a small screwdriver, and the housing should pop apart. The PCB then slides right out. You can remove the ribbon cable jumper too, it might get in the way during the next step.
Step 2: Solder Wires to 5V and GND
Looking at the back of the USB receptacle, the power and ground pins are the first and second pins from the left, respectively. However, and metal housing of the receptacle is also connected to ground. I found it was much easier to solder a ground wire to a pad that attaches the receptacle to the board.
Step 3: Reassembly
Slide the PCB back into the housing, snap both halves of the housing together, and you are done! The slot in the housing for the ribbon cable is plenty big enough to accommodate the new power wires. I added a barrel plug to the end of the power wires,to fit a programming board I made: