Hey mortimer . .
I had the same problem with the disc not ejecting, and then someone let me in on a little secret. Reboot the Mac, and hold the mouse button down. Depending on the mouse you use, it will either be left click or in the case of an apple mouse, just hold it down as if you were clicking on something.
This method bailed me out more than once!! Good luck, and let me know how you make out.
Bryan