Burn bootloader from Arduino Nano to Atmega chip
Here is one of the versions of the tutorial:
http://arduino.cc/en/Tutorial/ArduinoToBreadboard

This assumes the ArduinoISP sketch works on a nano. It should if its the nano also has an ATMega328 processor.

Connect the same pins by function as specified for the UNO. D10 to pin 1, D11 to pin 17, D12 to pin 18, and D13 to pin 19. These are the PDIP 28 package pin numbers. You will have to do something to the nano to deactivate reset when programming the bootloader. This is because it's wired to reset whenever anything connects to the serial port, which is great for loading in sketches, but you don't want it to reset when you go to program the bootloader. I believe the tutorial calls for putting a 10uf capacitor on the reset line of the uno. I have also seen versions calling for a resistor 110 ohms on reset to 5V. Disable reset after loading in the ArduinoISP sketch.