Running in CentOS 4.6, the following error output occurs when detecting the DVD:
Traceback (most recent call last):
File "discspan-0.1.2/discspan.py", line 170, in ?
drives = discover()
File "discspan-0.1.2/discspan.py", line 28, in discover
hal_obj = bus.get_object ('org.freedesktop.Hal', '/org/freedesktop/Hal/Manager')
AttributeError: SystemBus instance has no attribute 'get_object'
Better late than never... If I had to guess it would be that you don't have dbus-python installed? But that should have given an import error. Let me know if your still looking for a fix for this.