Thanks so much for your quick reply!
As usual, I've stated my question AND my problem incompletely. I have a set of nifty wallpapers designed to stretch across my dual monitors (
www.digitalblasphemy.com) but they must have the "Position" set to "Tile". (I was wrong; the default is "Stretch") I'm using gPhotoShow (
www.gphotoshow.com) to use these and others as ScreenSavers, too. One of the features of gPhotoShow is that it can set the last used ScreenSaver as wallpaper when you've finished enjoying the pretty pictures on the screen. But since a change of wallpaper resets the "Position" to "Stretch" it all gets messed up.
I see where you've directed me in [HKEY_CURRENT_USER\Control Panel\Desktop] but that seems to only reflect or change the current setting. Shouldn't I be making the changes in [HKEY_USERS\.DEFAULT\Control Panel\Desktop] to make "Tile" the default?