Extend the desktop?

I need your help!

I have a Compaq nx9010 laptop running XP Pro 2002 SP 3. I've connected a Dell flat screen monitor and want to use it instead of the laptop screen.

I've played with the display settings, have told it to extend the desktop to the 2nd monitor. But it doesn't work.

What I can do - I can move a window from the laptop off to the flat screen, and now when I open like the control panel - the pop-up window opens on the flat screen - not on the laptop.

It's acting like a 2nd monitor in addition to the laptop, and I want it to be instead of.

I've also pressed the FN F5 key, and the flat screen does 'blink', but it doesn't change my results.

I tried to upload screen shots of the monitor settings, but the files are too large. The screen shot does capture both screens.

What am I doing wrong?