Dual Monitor using laptop as second

I have a T-6836 with 4GB of RAM, running Vista 64 bit. I normally use an external 19" LCD connected to the analog monitor port as my display. I would like to occasionally use my laptop display as a second monitor. I have tried just toggling Alt-F4 but it doesn't do anything. My understanding is that I should be able to use that to have both displays active, then go into displays in Control Panel and optimize my resolution. Using control panel alone, I have been able to make my laptop monitor come alive with the wallpaper displayed but I don't seem to be able to switch to it to have another program displayed. Am I doing something wrong or is this an impossible task?

Thanks

 

Do you want to use the external display as your primary monitor and the laptop screen as the secondary? That is possible you just should have to change the external monitor to the primary in your graphics options.

If you want to use your laptop as a 2nd monitor (as for another computer) you can not do it with the VGA connection as its for output only.

 

Scratch that.

 

Yes, I want to use my external monitor as the primary and the laptop display as the secondary. When I go into display settings and check "extend the desktop to this monitor" for the second display, I get the wallpaper with no icons and the system behaves strangely. I can get the mouse cursor to go to the secondary and can click on the desktop but then can't move it back. I can open a program on the primary from the secondary but it doesn't display on the secondary.