A forum or Google search of the exact error message may turn up useful information.
What version of the game does he have (language / region / source)?
Is the prompt for a serial number during the install, or when trying to start the game after that?
Is the game being installed as administrator in Vista/Win7?
As far as I know, the English DVD versions of the game do not require a CD key or serial number to be typed in.
Try using a different optical drive, if available; I've seen the lowest drive letter one recommended, with comments that Securom (the copy protection used with the English DVD releases) can be picky if there are multiple optical drives.
Securom has a utility to remove / update / reinstall their drivers, and may have an FAQ or something on their site (they have D2:ED listed, but not this particular error, assuming it is coming form the copy protection).