: : 1) Is the Witch-King the same guy as the chief Nazgul that attacks Frodo on top of Weathertop?

: : 2) If so - why didn't Frodo's sword (taken from the Barrow) damage this Nazgul baddie the way Merry's sword (also taken from the Barrow) did?

: : 3) If the Witch-King is NOT the chief Nazgul that attacks Frodo on Weathertop - then who the heck WAS IT that got at Frodo in the FotR?

: : 4) And, just so I'm clear on this (and it's obvious that I'm not), the Witch-King is not the same guy as the Mouth of Sauron, right?

: : I know - these are terribly basic questions - and I apologize for asking. But, I just needed to clear this up once and for all.

: : Thanks!

: No need to apologise.

: 1)yes
: 2)good question, there is some debate over the nature of Merry's sword and the slaying of the Witch King at the battle of the Pellenor fields. Although it seems that Frodo didn't actually connect with the blow on Weathertop and merely tore the Witch Kings cloak.
: 3)n/a
: 4)yes indeed, the Witch King and the Mouth of Sauron are different characters

The mouth of Sauron is described as a Black Numenorean, corrupted during the Second Age. the power of the Lord of the Nazgul came from his possession of one of the Nine rings, hence the nine Black Riders, and their associated special powers.