Here is the key lines of code that you will need:

temp = analogRead(in_pin);

val =(float)temp * .0049 ;// val needs to be a float

There is 1023 steps when you analog read, every step is .0049 volts.

If your power supply will give more then 5 volts, you should divide the voltage with resistors(http://en.wikipedia.org/wiki/Voltage_divider).

If you divide your voltage in 3 or 2, you should multiply val by 3 or 2.

Hope I helped.