If you are doing an important task (say downloading a file) and don't want to put the computer to sleep by closing the lid, you can use the app SleepLess (close the lid, then use the "Detect Displays" option to disable the internal LCD). However, I highly recommend that you reopen the lid after you have re-awakened the Powerbook from sleep (the internal LCD will be off). The Powerbook Titanium releases a large amount of heat though the keyboard, and keeping the lid closed is bad for the LCD and the computer.