I have an Intel-based Macbook with Mac OS X 10.5.4. I mostly work on the macbook at the office with an external monitor, keyboard and mouse. I was looking for the solution to keep the lid closed while working with an external monitor. It turns out that you really don't need an additional software in this case. When you close the lid the computer goes into sleep mode. Then you press any key on external keyboard and it wakes up without switching on macbook monitor. Now you can work on external monitor with macbook lid closed and macbook display turned off. You can open the lid but macbook display will be still asleep. If you really need to turn the macbook display on - just click "detect displays" in the external monitor menu on the status bar (you will find this option if you have checked "show display in the menu bar" option in Displays preferences). After you have both displays working, if you want to use sleep mode again - just close the lid - both monitors and computer will go into sleep mode again.