You are not sure if one of the installation CD's (or the DVD) might have a physical defect. You would like to check on this.
Run the following command as root:
dd if=/dev/cdrom of=/dev/null
(If the symbolic link /dev/cdrom doesn't exist, or is incorrect, then you have to replace /dev/cdrom by the appropriate device file. E.g. /dev/hdc if your CD/DVD drive is connected to the master of the secondary IDE port. This will also be the case, if you don't have Linux installed already, and therfore have to use the rescue system to do the checking.)
If the media is fine, you should get a result like the following:
linux:~ # dd if=/dev/cdrom of=/dev/null 1316996+0 records in 1316996+0 records out
If, on the other hand, a physical defect on the media prevents the data from being successfully read, you will get an error message.