Novice libdvdread problem

Hello! I am attempting to play DVDs on my new Dell Inspiron 600m 
notebook. This is what happens:

ogle -u cli /dev/dvd
libdvdread: Using libdvdcss version 1.2.8 for DVD access
libdvdread: Could not open /dev/dvd with libdvdcss.
libdvdread: Can't open /dev/dvd for reading
ERROR[ogle_nav]: faild to open/read the DVD
DVDSetDVDRoot:: Root not set

I have tried the obvious solutions that are given to similar problems - 
the symlink exists and points to the correct drive, it's not a 
permissions problem, etc.

'ogle --check' produces:

/dev/dvd -> /dev/hdc
Valid DVD devices:
WARNING: No DVD devices found

As might be expected, VLC also fails with a similar message.

I am running Slack 9.1 with a 2.4.22 kernel. Test disc was "Monty Python 
and the Holy Grail" - although the problem must be deeper than that.

Thanks!