That's what the computer will do if it can't read the disc. The fact that it spits it out so quickly means it REALLY can't read the disc.
Assuming it's not just a bad DVD as suggested, it's pretty certain either your optical drive is bad, or the lens is very dirty (which happened to my MBP). If you have a lens cleaning disc around, there's no harm in trying it, since it's not working anyway. Otherwise, call Apple/bring it in to a store if it's still under warranty, or replace it on your own if it's not. At least they're not all that expensive, though getting the drive in isn't easy.