Switch Camera On Button Press?

I have a sniper rifle which is a child object of the main camera on fps controller and then I have a camera which is a child object of the sniper rifle. What I want to do is when you click the right mouse button, you go from looking through the main camera to looking through the other camera, and when you click the right mouse button again you switch back to looking through the main camera. Can anyone help me with this?

Twist answer- only have one camera!

Then, have two transforms which are managed separately- one on the scope, and one for the main character. Treat these transforms the same way you would use a camera in terms of movement etc., and then when you want to change camera, do this-

Camera.main.transform.parent = transformYouWantToChangeTo;
Camera.main.transform.localPosition = Vector3.zero;
Camera.main.transform.localRotation = Quaternion.identity;

use a lerp:
http://unity3d.com/support/documentation/ScriptReference/Quaternion.Lerp.html

and assign the result quaternion to your camera