Just thought I'd share another way to move / scale the image planes.

After you create the Imageplane
- Select it (View->Image Plane->Image Plane Attributes).
- Open the Channel Box if its not displayed.

Now you can change the the following attributes:

Center X, Center Y, Center Z - Position of the Image plane in the viewport
Width, Height - Scaling of the Image Plane

To adjust these values with the mouse, click on an attribute name to hilight it, and then drag with your Middle Mouse button inside the viewport.

You have to adjust each value seperately (X, Y, Z), but its easier than editing the values by hand.