SleepTight provides a simple way to lock your machine when it goes to sleep or lock from a keyboard hotkey.
Surprisingly, MacOS X 10.2’s built in screensaver does not start automatically when the machine goes to sleep. Since the screensaver is the only Apple-supplied method of locking your machine without logging out, this means that a machine which has been put to sleep may wake up unlocked if the screensaver did not start on its own before the sleep timeout. This is especially frustrating for PowerBook users, who typically put their machines to sleep by closing the lid. Since the lid closure doesn’t start the screensaver, the PowerBook will awaken unlocked. Apple has fixed this in MacOS X 10.3 (Panther).
For MacOS X 10.2 (Jaguar). Please note that MacOS X 10.3 (Panther) is not supported because it already incorporates lock on sleep functionality.