Not sure if this will work in this situation, but hold down "CMD-X" on startup and it should force booting into OS-X.
Otherwise, hold down "option" on power-up and keep it pressed until you get a selection of boot volumes.
Try holding down the trackpad button on power-up to eject CD.
I'll be interested in what happens, as I'll be installing XP through BootCamp soon. (as soon as the store gets my 17" C2D in....)