Is there a way to make a rectangular prism using the insert shapes feature of powerpoint? I can make a prism out of the cube, but that only gives me control of 2 out of the 3 dimensions.
There is an alternative way of achieving this which has some advantages and some disadvantages depending on what you are using it for. The steps are as follows:
I believe that you can control all the dimensions of a cube.
Below is a screen-capture from Office 2007. There are handles to handle every dimension.