BtProx is a small Windows application working both under Windows XP and Vista. I never tested it under Windows 2000, but there's no reason why it should not work. It locks your computer when you go away from it. How is it done.
It locks on one of your Bluetooth devices which are paired to the the machine. When you walk away from the computer the device is disconnected and the computer is locked after timeout. It is possible to run a single application together with the lock. This application may be your favorite script dismounting network drives, erasing those dirty files from the desktop or anything else. The program sits in Windows tray showing its current status with tray icon and tooltip baloons.