In which case, you've got one of three problems I can think of:
1) The lens in the optical drive is dirty, causing read errors. This actually happened to my first-gen MBP 17" recently. In this case a cleaning disc might fix it (did for me).
2) The disc itself is bad. This would be apparent if other discs work fine, and particularly if that one always has trouble in the same spot or behaves similarly on another computer or set-top player.
3) The optical drive is dying. Can definitely happen, no much to do but replace it. The drives themselves aren't outrageously expensive, but they can be a hassle to install if you're not comfortable digging around in the guts of a laptop.