Hey, I attempted to set up dual screen in linux yesterday, and managed eventually, then thought better of it (the screen was really bought for my other computers) because i couldn't easily just take it out and put it back when i wanted (I assume, i love how apple can do this, but anyway).
The primary screen is a 23" apple Cinema HD one at 1920x1200 and the other one I used was an LG L1954TQ 19" 1280x1024. Its back to running at one screen now and it works at 1920x1200 but the desktop background seems to be at 1280x1024 and then just has white space to fill up the rest. Using KDE4, the widgets thing appears on the top left of the 1280x1024 area, so near the middle of the actual screen.

Does anyone know how to make it go back to the way it was?

Actually, a thought just dawned on me...reset KDE4 config? But I can't remember how to do that if someone could enlighten me and/or tell me if that would work or something that would!