Internal drives are 3 1/2" drive bays used for hard drives and anything else you could fit in them. External drive bays are both 3 1/2" and 5 1/4" sizes. The smaller is used for floppy drives and other accessories you need access to such as fan controllers. 5 1/4" bays are used for optical drives, or in laymens terms CD/DVD drives. Fan controllers and other accessories can fit in these as well.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w