I'd just converted from slack to ubuntu 7.10 last week. The
same thing happened to me, but I'd restarted the install, & it
went fine. I think doing Alt+F4 or Alt+F5 will give you a screen
of what's happening. If you're lucky, you'll see exactly what's
up.

A co-worker had also hit this snag with his video car. Sorry,
I only remember that it was an ATI card.

There's also the possibility your disk is damaged, obviously.

I wounder if you burned the ISO image too fast. Maybe burn the ISO at a nice low
speed like at 10X and all so compare the check sums too. There is a lot of data
on the CD and burn it too fast. The data that is needed may be bad.