You should verify how the current switch is connected into the circuit. If power is fed to the light then you would have a switch loop. The box were the light is mounted would have two cables connected and the switch would only have one cable. If this is how it is wired then all you would have to do is fish a piece of 14-3 (if it's a 15 amp circuit) through the wall from the old switch box to the new switch box and wire up two three way switches.
So this is a start...
So this is a start...