Open the LMCE admin page.
Click on Advanced->configuration->devices in the green bar at the top of the right panel.
You should see a list of "My devices" in the lower left hand pane.
This will display several items: DCERouter, App Server, Generic PC as MD
In my case, I selected "Generic PC as MD". It depends what your box during the setup.
That will open a list of devices such as: OnScreen Orbiter, HAL, GeForce or TNT2
Select "OnScreen Orbiter"
Select the "Disk Drive" option
Scroll down to the bottom of the right page. Under the "Device data" section you should see the name of the drive (/dev/cdrom). Change it to /dev/dvd (assuming that's the path to your DVD)