Hi,
The 'files' in /dev are an interface to devices and 'cd /dev/hdb' has no meaning - in any event /dev/hdb is a 'file' not a directory. Under the linux virtual filesystem everything is represented as a file/directory somewhere under the root '/'. So, to access files on a CD drive you would mount the device at a mount point in the directory tree of your choice - basically as per fortytwo's answer above. You might have to specify the filesystem type (iso9660) though :
mount /dev/hdb -t iso9660 /mnt/cdrom
Incidentally, if you end up wanting to play audio cds, etc., these do NOT need to be mounted. You just configure the player to access the device directly.
Hope this helps