1)  Power down your machine (remember shutdown!!! ;-))
2)  Open it up (you'll prob. need Torx screwdrivers).
3)  On the side of the drive, you should see a small rectangular piece
    of plastic.  Gently pry it off... it should come off quite easily.
4)  The aforementioned piece of plastic covers a hole, which houses a
    small dial.  Spinning this dial ejects the tape.
5)  Replace plastic piece, close machine... and Bob's your uncle.

p.s.  The dial has very little torque (ie. the tape comes out quite
slowly, but you can see it move.  It'll take about 2-3 minutes of
spinning before the tape comes out.