What program are you using? Most of the time you will want to create a symlink to the actual device.. like /dev/dvd --> /dev/hdc
Depending on what controller you have it on will tell you the actual device.
hda > Primary IDE
hdb > Primary Secondary IDE
hdc > Secondary IDE
hdd > Secondary Secondary IDE
And remember, you don't mount media DVD's, you load up the program like Totem or MPlayer and just play them, pointing to the device.