Theres an internal connection within the computer that connects both of your drives to the motherboard.
The connection is through an IDE cable. There are two ends and there is a split within the cable where there is another connection.
So you have two connections to which the drives can connect to...Going through the one cable to you motherboard.
Because the connections are on the same cable thats your problem.
The easist way is to buy another cable and connect that to the other connection on your motherboard.
So each drive has its own IDE cable.
At the moment it is being shared, thats why the message pop up.
If you copy and CD the data is being sent down the IDE cable and the other Drive copys the data. The speed of which will be slow so it could cause error on the CD.
If you have two seperate IDE cables it will befaster and there will be no errors (not guranteed).
Its best to copy the data of the CD onto your hardrive then copy the data to the CD.