Pan Camera with mouse?

I want to pan my orthographic camera with my mouse. I only want it to move X and Y. I want Z to stay the same. I script in javascript. Any ideas on how to do this? Thanks in advanced.

public var mouseSensitivity : float = 1.0;
private var lastPosition : Vector3;

function Update()
{
    if (Input.GetMouseButtonDown(0))
    {
        lastPosition = Input.mousePosition;
    }

    if (Input.GetMouseButton(0))
    {
        var delta : Vector3 = Input.mousePosition - lastPosition;
        transform.Translate(delta.x * mouseSensitivity, delta.y * mouseSensitivity, 0);
        lastPosition = Input.mousePosition;
    }
}

I used a value of mouseSensitivity around 0.01f. This will definitely need to vary with the scale of your scene.