Gary O'Reilly

Answer: The "Witch King" is just that: A Witch King. Before he became a Nazgul, he was still a mightly wizard in his own right, and a feared King in his own time (note that the only reason Merry's sword hurts him is because, when it was made, it was made specifically to attack him, showing that at some point people had feared him enough to put magic into weapons against him). As a Nazgul, his powers can only have increased. As a side note, in the books, Gandalf and the cheif nazgul never actually meet in combat, they see each other and prepare for it, but the Nazgul is driven off when the Rohan charge without them actually fighting.

Gary O'Reilly

Answer: Guard it from who? One of the premises of the whole plot is that Sauron simply cannot believe that someone would want to destroy the ring rather than use it themself. That's why the plan succeeded, and that's the only reason it succeeded. The loss of the ring forced Sauron to make his move early (i.e. sending out his armies sooner than he would have wanted) to stop whoever was using the ring (the only possibility in his mind) from gaining too much power. So who would want to go into Mt. Doom? Besides the fact they'd have to get INTO Mordor first (something which Sauron would have laughed at anyway) they could do nothing there anyway, unless they were there to destroy the ring, which is something Sauron didn't even consider. It'd just be an utter waste of man (orc?)power.

Gary O'Reilly