How can I acces unformatted cd/dvd with data on

[Michael Schwinck <schwinck@web.de>]

I am running etch (last updated in April 2007) and trying to read a dvd
which contains one big file (no file system). - It has been written by a
dvd-recorder (connected to a tv set). But also writing e.g. a tar
archive to a cd leads to the same issue:
/var/log/messages extract 
.. 15:09:18 localhost kernel: hda: media error (blank): status=0x51
    { DriveReady SeekComplete Error }
.. 15:09:18 localhost kernel: hda: media error (blank): error=0x84
   { AbortedCommand LastFailedSense=0x08 }Sep 20 15:09:18 localhost
   kernel: ide: failed opcode was: unknown
.. 15:09:18 localhost kernel: ATAPI device hda:
.. 15:09:18 localhost kernel:   Error: Blank check -- (Sense key=0x08)
.. 15:09:18 localhost kernel:   "28 00 00 00 00 00 00 00 01 00 00 00 00
   00 00 00 "
.. 15:09:18 localhost kernel: end_request: I/O error, dev hda, sector 0

What I tried is to read some bytes of the dvd/cd issuing 
"dd if=/dev/cdrom of=./tf bs=512 count=1" (you can vary "bs" that does
not change anything).

I assume /dev/cdrom corresponds with a block device, however the dvd/cd
is unformatted, so data can not be accessed this way.

Any ideas how to read the data?