How can I wire up an guitar pickup to the Arduino so that I can detect sound?
The arduino just needs to know if the pickup is/isn't being played, it'll act like a switch
Am I right to assume it's the same as wiring a pc microphone for exemple?
According to wiki, guitar pickup outputs 100 mV - 1V signal. That makes interfacing with arduino very simple, a few resistors + cap. Look at the right drawings, headphones / speakers input : http://coolarduino.wordpress.com/2012/06/22/audio-input-to-arduino/
And here, how to measure AC: http://coolarduino.wordpress.com/2013/01/09/audio-vu-meter/
You'll want to connect the signal to an analog input. Then read the ADC and compare to a preset threshold. (You don't want it too sensitive, or noise will trigger your software). Setting the threshold will require some experimentation.
There is one complication... The guitar signal is AC (it goes positive and negative), and you cannot put negative voltages into the Arduino. The low current capability of a guiter pickup is (probably) not going to damage the Arduino, but the sound-signal will be distorted.
You can bias the input with a pair of resistors and (1 or 2 Meg should be about right for a guitar) and a capacitor. I like to use a [u]Peak Detector[/u], but it's more parts and it requires a +/- power supply for the op-amp.