Thanks.

How do I get a picture INTO my gallery? Which folder is that?
I had a couple in there -- no idea how they got there. I selected one and saw a box I could slide around to pick what PART of the picture would become the wallpaper. I did that, but that essentially means there is no way to make a panoramic picture the wallpaper and have each of the five Home screen "panes" show a different piece of it (unless I can hack around the UI, and the use of Gallery for wallpaper picking).
The wallpaper also seems to use just the top HALF of the image I designated with the "picker box" in Gallery.

My idea was to create a wallpaper image from five different images, in one file. With watermarked labels for REFERENCE MEDIA MAIN UTILS and GAMES, so that the page I was currently on would be intuitive from the background and confirmed by the watermark. Maybe I'm reaching too far, but it seems like a rational thing to do. Having the wallpaper shift slightly with each pane makes it SEEM possible, I just don't see a way to do it.