Sorry, I just came back to this topic and think I may have ruffled some feathers. My apologies to EliteLevel, I should not have called you a whiney bitch. Your question is a very fair one, and its something that I haven't thought about in quite a while. I have just become jaded over years of people saying things like, "Why didn't they just get the eagles to drop the ring in Mount Doom?"
To answer your subsequent questions, the Nazgul were taken completely by surprise. I can't stress enough how much the overconfidence factor plays a part in this. Remember that the Hobbits (with an injured Frodo) and Strider were about 14 days away from Rivendell. The Witch King had managed to give Frodo what should have been a mortal wound, had he not had the mental fortitude which he possessed (which is why he was the ring bearer). They had expected to easily take the ring at Weathertop but were met instead by the most powerful human in existence at the time, as well as 4 incredibly brave Hobbits, armed with the knowledge of what they protected, and blades which they foraged from the Barrow Wights, which were specifically designed to battle against the Nazgul in days gone by. And even after Frodo had been stabbed, he screamed Elbereth! O Gilthoniel! Imagine the shock of the Witch King hearing these words uttered by someone like that, and then getting driven back by the most powerful being from the race of men in 3000 years. They expected to win easily, and even after getting driven back, they had 14 days to get the ring, so once again, they were confident that they would triumph.
