I added a thumbnail image so that you can load five images at a time rather than four. I also resized the images to be smaller, then called the smaller image size for the thumbnails, and increased the image size for main view.
The images load as expected. The forward and backward buttons will advance or reverse (respectively) five images at a time. When you reach the end of the image list and hit the forward button, it loops back to the beginning. Likewise, clicking the backward button while at the beginning of the loop will take you backwards to the end of the image set. Last, I positioned the buttons farther apart than in the example--I'm a usability person by trade, so having them too close together was a pet peeve of mine. =)
I was ecstatic to both get it to work, and to be able to modify the code and get the modifications to work. In fact, ecstatic doesn't even begin to cover it. I'm beyond thrilled to have been able to do modifications that both reduce the number of screens the user would have to scroll through (by going through 5 images at a time) and to reduce the bandwidth needed for downloading the images. To me, these are even useful modifications, so I find that thrilling. Thanks for all your help!