Screen dimming

Is there an app out there that makes it so when i connect an external display to my powerbook it automaticly dims the internal screen to a user set brightness and then when you disconnect the display it goes back to normal?

thanks
--Ben

if you are using a external mouse and keyboard. you can close the lid of the powerbook. when it goes to sleep move you mouse or tap the keyboard and ti will wake up.. mmost people say this is bad.. but on the powerbook it is ok apple tell you hwo to do it in the manual.. ( this will not work for an ibook)
as for software that would make it dim i have never seen such