a relay or another way?

Hi, I am a new member with very little knowledge of electronics and would appreciate any input from more knowledgeable members.

I am trying to use the Arduino Uno to send a signal into Max4Live to trigger a sample in Ableton Live.
The way I want to create the initial signal is to make this simple circuit;
My guitar, with a steel string is pressed down as normal onto one of the frets to make a note as normal,
a copper wire is wrapped around the fretboard to provide a conductive strip,
one crocadile clip is attached to the guitar string at the headstock (where the tuning keys are)
a length of copper wire extends from this crocadile clip to the Arduino.
Another crocadile clip is attached to the copper wire wrapped around the fretboard and extended to the Arduino to complete the circuit when the guitar string is pressed onto the conductive strip (wire).

My question is what do I need to use and how do I connect to the Arduino Uno to send a simple on/off state?
I want to be able to play the notes as normal on the guitar and just use a trigger point provided by this arrangement to activate the circuit - on then off, with each press of the string on that particular fret while continuing to play.
Any ideas? can this be done?

Connect the string to an arduino input pin. Connect the fret to a ground pin. Run a simple read the input pin & react program:

byte pinX = 2; // pin D2 for instance
byte pin13 = 13; // onboard LED on D13

void setup(){
pinMode (pinX, INPUT);
digitalWrite pinX, HIGH); // turn on internal pullup resistor

pinMode (pin13, OUTPUT);
digitalWrite (pin13, LOW); // turn the LED off to start
} // end void setup

void loop(){
// now when string is pressed to the fret, the input pin is connected to ground.
if ( digitalRead (pinX) == LOW ){
// when the pin is grounded turn on the onboard LED
digitalWrite (pin13, HIGH);
// otherwise turn the LED off
digitalWrite (pin13, LOW);
} // end void loop

Hi CrossRoads, thanks for your help. I tried your code but the Arduino expected a ';' before ')' token. when I added this it then expected a primary-expression before ')' token. Do you know what this means please?

It means you missed out a ; in the line above where the error is flagged.

Thanks Grumpy Mike.
I have the code working now, the next thing I would like to do with this set up is to make the Arduino trigger an audio sample instead of just turning the led on and off.
Does anyone know how to change the if/else code to make this happen?
I have Max MSP, Maxuino, Firmata and Ableton Live but it seems that I could achieve what I want with just the Arduino. Is this possible?

You should know that your guitar string "switch" is contact bouncy as all heck.
For an led, quick micro flashes are no problem. If you are triggering something or counting something
that's a different story.
To check this try modifying your code to count the fret triggerings.
Press the string twice. You will get MANY counts.
De-bouncing software or hardware is in many places on this forum.

Good luck. Like your attitude.

Well, to try to clarify, what I really want to do is this - I want the guitar string and contact strip switch to send a signal from the Arduino into Maxuino which is running in Ableton Live.
When Ableton Live successfully receives the signal it will then trigger an audio sample each time I press the guitar string down onto the fret containing the contact strip.
The code above from CrossRoads works perfectly to turn the led on and off, but to send a signal from Arduino into Maxuino I have to use Standard Firmata code and this is now the problem.
The code above works within Arduino but Maxuino requires different code to trigger events in Ableton Live.
Any Ideas?

You do NOT have to use Firmata to do what you want.
Those two programs have to do some of the work. That is they recieve the message, and take the appropriate action. This is not an arduino problem but one with the code in Ableton.