Turn off monitor on del Vostro 1500 while laptop in use?

"Fn-DownArrow (type several times) will lower the backlight. That's a major source of power drain.

Other Dells I've had have supported turning off the LCD with a different Fn key, but I don't have a Vostro 1500 in front of me to see if that works.

Fn-F8 (blue label is CRT/LCD) should switch to external display, but I'm not sure it'll stick with that if there is no actual external display.
It might be that an enterprising friend with a VGA connector and a soldering iron could make a stub that looks enough like an external monitor to encourage your LCD to stay off."

I know this is 1 1/2 yrs ago, but for those still looking for a solution for this. I've read you need only to connect an external keyboard and mouse and close the lid before it fully boots up or was that shortly after. And that should reroute your graphics to your display.

"You could use MonitorES:

MonitorES is a small windows utility that helps you to turnoff monitor display when you lock down your machine.Also when you lock your machine, it will pause all your running media programs & set your IM status message to ""Away"" / Custom message(via options) and restore it back to normal when you back.
According to this research statistics we could save lot of energy by turning off monitor display."