This "problem" really started to annoy me recently; whenever I connected my laptop to a base station at home which is connected to a larger external monitor Vista would always assume that my laptop screen was the best primary display, go figure. The primary display  is the display where you access the Start menu in Windows.

Often the Mobility Center pops up and you know the drill; Vista asks if you want to see the same information on each screen or show a separate desktop on the external display etc...

However if you want to ensure that the larger external display is considered the primary for the desktop and the laptop LCD or alternate display  is the secondary follow these steps:

1. Wait for the prompt to configure the external display
2. This can be forced to open through Mobility Center (Windows key + X or accessible through Control Panel). Select the "Connect Display" button.
3. Choose to display desktop on External monitor only, this is the one you want to make the primary display.
4. Now right click on the desktop and select "Personalize", then select Display Properties. This option can also be accessed through Control Panel.

a. When display properties dialogue is displayed you need to select the second screen that you wish to extend onto, in my case its the generic LCD panel of the laptop.

b. Once selected you can then check the box labelled "Extend the desktop onto this monitor"

In this dialogue also remember to drag the second monitor to the left or right of the primary so that your mouse has a natural method of entering the desktop field of vision of the second screen i.e. to the left or the right. Then your mouse can predictably enter the desktop of the second display. You can also position this field of vision entry point to be corner to corner of each display. Therefore your mouse will not accidentally leave the primary desktop unless you move your mouse to the second display through this specific entry point.

HTH

John Hodgson
HP Australia