I might be missing the point here, Joanna, but...
You don't have to tell your PC to ignore one drive and only "see" the other. When you put a CD or DVD in the drive you want to use, it either autoplays or you access the files on it from My Computer under your Start Menu (then right-clicking on the appropriate drive icon and selecting Explore). And if you want to write something to the disk in that drive, the software you are using asks you to tell it what drive you want to copy to.