How do I force eject an install dvd on an imac who's HD was just erased in order to do a clean install?

I was trying to do a clean install on an iMac G5,

it was running 10.3. So when I put the DVD in and booted to DVD I went to untilities and then Disc utility and erased the hard drive in order to do a clean install.

The problem now is that the DVD I'm using is an upgrade DVD and it needs to see 10.3.9 in order to let itself install. Well, I just deleted it and now I can't eject this disc so that I can put a different one in that does not require a prior operating system in order to install.

My end goal is to do a clean install of 10.5, the latest operation system that this iMac will take.

I would really appreciate any suggestions.

Tim