I am struggling with this, too...
When I try to use the software update gui app, it kept asking me to put the disc 1 in the /dev/hdb drive. No matter what, it would never access the disc when I put it in.
I'm not really sure what the problem is, though. I haven't done anything with the cdrom drive after the original install. When I checked harddrake, it said the cdrom was on /dev/sc0. I really don't think this is a scsi cdrom drive, though. I don't have a scsi adapter in this computer.
Just another finicky and annoying thing I'll probably spend several hours trying to figure out. Or, I'll just avoid updating any packages from the cdrom for the time being until my annoyance pushes me to the point of dealing with the problem.