How eject Frozen Install DVD

Using SL Install DVD purchased from Apple the install went to the 1st step after 'sign this agreement' (which I did) then the next window - the

INSTALL Mac OSX - select the disc where you want to install Mac OS X

and under that is the picture of my Mac with a yellow triangle

"Mac os X can not startup from this disc"

unable to get out of that scenario -- can only go back to language selection window with ONLY an option to continue.

pressed every key on keyboard and cannot go back from that or whatever .

Not sure what to do

screen is frozen at that window from the install DVD (which worked okay last time it was used on a different mac year or so ago)

Is there a way to force it to eject the dvd?

and shut down

or?????