Internal and External information
Internal drives require the computer case to be opened. If you are replacing a drive, you will have to remove the old one and insert the new one. If you are installing one and not replacing a drive, you will have to add it to an empty spot on the computer. Before installing the drive, read safety instructions Click here for instructions on installing computer parts
External drives are connected via USB, 1394, or parallel. This does not require the system to be opened for the install. USB drives can be connected while the system is turned on. I believe 1394 drives can be connected while system is on (but I am not sure). Connecting a drive to the Parallel port will require the system to be off while you connect it (or you can fry the motherboard).
As far as the speed of the drive and the speed capability of the disks, A drive can write to any speed up to the designated speed of that drive. if the drive is a 16X drive, it can write to a 2x, 4x, 12x all the way to a 16x. If the disk is a 52x speed capable disk and the drive can only write at 48x, you can still use the CD. It will burn at 48x and not 52x.