Fix Popup Window Size in osCommerce

On the product pages of my oscommerce website ([login to view URL]) when the image is clicked (to enlarge), the popup window is not resizing to fit the image. For example, on this page [login to view URL] I click the image and a window pops up that's only 100 x 100. In Windows, the window is only 100 pixels too short. On the mac, the window size is not dynamic at all, and only displays 100 x 100.