Or press the Windows Key and X (its a shortcut to mobility centre).
Start>Control Panel>Hardware and Sound (under Devices and Printers).
There should be an option in there for the synaptics touchpad including a way to turn it off.
check the system tray icons on right lower corner of the screen.You might have to click the little arrow sign to see more icons.One of the icons "Dell Touchpad" opens up the software that controls the touchpad.There should be an option to deactivate the touchpad.I've got an inspiron 1545 but I think that you have similar software installed.
Nope again. There's no icon in the system tray for the touchpad. It's hard to believe that it's so hard to find a way to disable this touchpad. I've been looking for a long time and finally decided to ask for help. It is nowhere to be found.
While I don't have your model so can't confirm, every Dell I have had with the synpatics touchpad has had the icon in the system tray.
Try reinstalling the driver <ADMIN NOTE: Broken link has been removed from this post by Dell> to see if it brings the icon up.