Have a (company president's) Dell 620, running through a Dell dock into a ViewSonic monitor. Recently, when the laptop is mounted to the dock, the attached monitor shows up as the laptop's wide screen setting (like a picture box). I read through some issues here and tried to find a full screen switch but couldn't find any.
I did find a Dell utility for making such settings, but this one stretches the monitor's setting when it's on the laptop, and it only offers two resultions - 800x600 or 1240x768 - through the utility when both monitors are active. If I uncheck the "full screen" switch in the Dell utility, then the laptop display the monitor's 800x600 and doesn't use the wide screen.
(and like I say about company president, remember Sam Breakstone?...)