GNUMPlayer-1.0rc2.pkg is not a disk image with a valid file system... it's simply a file!
You need to create an image.. either ISO9660 or UDF.
EDIT: Woah, According to Wikipedia DVD+RW can be used like a normal block device.. you may be able to entirely eliminate cdrtools from the scenario and "newfs" it like any other device. (FFS file system even?)..
I don't know how Solaris names it's device nodes so I can't help you with that.
