>>Win7 can cycle through screen backgrounds every few minutes. Check your settings under personalization.
>
>I did right click, Personalize, but after that, it is not obvious where to go to see something about it. Where have you found it exactly?

I'm stuck at a client site with an XP machine today, so I can't tell you exactly.

I think it works like this..

http://www.nirmaltv.com/2009/05/03/how-to-change-desktop-wallpaper-quickly-in-windows-7/