Gandalf Vs. The Witch King

[Essex]

I'm getting confused as book Gandalf the Grey drives four Nazgul from Weathertop; movie Gandalf the Grey or White does not encounter any Nazgul until he and Pippin reach Minas Tirith. The Witch-King could have overestimated his own abilities; Gandalf could have underestimated his. Plus, like many superhero brawls, assume that Gandalf can easily hold his own against the 'powered up' Witch-King. Assume that Gandalf even knows this, and also knows that according to the prophecy that he himself will not slay the King of Angmar. So I guess he shouldn't have anything to fear? But the Witch-King, being on the evil side, could attack Gandalf via the hobbits, Theoden, other innocents, etc., and this thought may concern Gandalf. He may know that, regardless of the Witch-King's boasting, that the only way that Gandalf could be overcome would be for the Witch-King to make him submit, drop his staff as it were, as the WK would have taken Merry or Pip hostage.

But Gandalf has the body of a human and can be killed with a sword though, correct? (esp a flaming one LOL) - so he CAN be beaten, even if he IS stronger than the WK........

PS - in the weapons and warfare movie tie-in book - it states that the sword Merry uses on the Witch King is Thedoen's sword he had as a child. Why PJ wanted to do this, he only knows........

The way I approach the film is that the stuff we do not see in the movies still actually happens. ok sometimes we have some conflicts, but to me, the movie hobbits DID meet Tom Bombadil, we just didn't see it. so merry gets his sword from the barrow-wights in my mind. (he was just given an extra one by Aragorn LOL) And therefore you could also say that movie Gandalf fought off the Nazgul on weathertop too.....

PS - Movie wise, how can you convey the brilliant text of Tolkien explaining why the Witch King was defeated? I suppose we could have Gandalf mention it later, but then how would HE know?