Gizmo - In fact, if you don't know what SCSI is, I'm gonna say stay away from SATA too. Just go with the good-ol ATA drives. Faithful, fast, dependable, cheap, simple.
Major:
IDE stands for Integrated Drive Electronics
EIDE stands for Enhanced Integrated Drive Electronics
EIDE is the updated version of IDE (faster transmission times, protocols, etc).
For the record, though, plain IDE is legacy and not made anymore (except by special mf and need). When people/merchants refer to a drive as IDE, today, they really mean EIDE.
Unless your system is like 8 years old (or more) you probably don't need to worry about it.