Rex, the source for swap_viewer is already available and inside our developer's forum under the same name thread. I never cleaned it up (it's messy), but it basically expands on Penguin's original swap tool with a window's gooey for easy use and for individual image viewing.
You're more than welcome to it if you can utilize any of the code from it. If I remember, I used an owner-drawn button for the display which is updated while flipping thru the textures. It's an easy method & requires little code. I'm fairly certain the released code also has the shift code I used for displaying the raw bumpmaps & for displaying the 16bit textures.