Should only need to Eject Disk (Cmd+E) after selecting the disk icon, or use the eject button on the Apple extended USB keyboard. The problem has been known to happen in OS 9 as well...You may be able to push a paper clip into the tiny hole above and to the right of the disk entry. If that doesn't work, the final solution is to press the button on the Zip drive -- the one hidden behind the plastic bezel. You may want to remove the bezel and drill a pin hole in order to facilitate punching that puppy out in the future.