By you text, you copied the .iso file to the CD, BUT did not BURN the
.iso image to the CD. Copying just gives you a dumb file on the CD.
"Burning the image" gives you a bootable CD with a filesystem filled
with all the stuff you need to do the installation. Go back to your CD
software and look for "Burn Image", or something to that effect, don't
just copy to file to a blank. Been bitten by this concept myself.
Matt