Lawrence,
Why don't u try or check out the following :-
Do a diskinfo on the specified device file and see if it is a DVD-ROM as well as check if the size of the disk is being shown to make sure that the drive is actually detecting ur disk.
Next thing is have you created the mount point?
Also do a diskinfo on /dev/rdsk/c0t0d0 cez typically that is the drive you would be concerned with.
If not, try mounting the DVD with persistent DSF if u r using v3 by doing an ioscan -m dsf.
Best of luck,
Read, read and read... Then read again until you read "between the lines".....