Hello Chris -
Only the main images magnifies. Here are the instructions from the doc:
Each product can have up to 10 images associated with it: 4 thumbnails, 5 full images, and 1 zoom image. At least one full-size image is required. That full-size image is specified in the product update section under the “Product Images” tab when creating or editing a new product. This image can be up to 460px wide by 375 px high, without modifying the CSS.
For the zoom function of the main photo, put a file in the “Add Image File” dialog (for the product) with a title of “Zoom”. With the product open for editing, click “Add Image File” as shown below. Upload the file, set the file to unpublished, and be sure to not resize. For best results, the Zoom image should be about twice the width and height of the full-size image.
You add your primary image for the product using the regular Virtuemart functionality. The zoom image is added as an additional picture file, must be unpublished, and must have the file title of "Zoom." Not the filename of "Zoom," but the file title.
I have attached a screen capture which shows how all of our images are set up for one of our installs.