If you didn't understand my prevois post:
FDD stands for Floppy Disk Drive. Either the small 3,5" or the large 5,25" one (that's the one you're asking about).
BIOS is the mini-program on your motherboard that controls most of the computer's function.
The IDE cable is the cable used to connect drives to the computer's motherboard. There are two sorts of these - one for hard drives and CD drives and one for floppies. The floppy IDE cable must have certain sort of connectors for you to be able to connect it to the 5,25" drive.
As I said, the 5,25" floppy drive is NOT called "Drive B". It's just 5,25" FDD, not much different from the smaller 3,5" one, really.
Read some on these things on wikipedia:
http://en.wikipedia.org/wiki/Floppy_disk
However, seeing as even 8 years ago - when I have found out that a game I bought was on 5,25" FDD's - this format was on decline, you might have trouble finding a 5,25" drive these days, not to mention that most of your brother's 5,25" floppies will probably be degraded beyond recovery.