Peggy Sue,
this is straight from CS3 Help:

Quote:

Progressive Displays the image progressively in a web browser. The image appears as a series of overlays, enabling viewers to see a low-resolution version of the image before it downloads completely. The Progressive option requires use of the Optimized JPEG format.
Note: Progressive JPEGs require more RAM for viewing and are not supported by some browsers.



Hope that helps,

Jim

Jim Garvie
www.jagphoto.biz