Those green ghosts are the Oathbreakers. In the war of the Second Age, also known as the Last Alliance between Elves and Men, Isildur, heir to the throne of Gondor, asked the men of the mountains and their king to swear an oath to him to fight in that war against Sauron. These men were chickens so in the end they didn't come, so Isildur cursed them to never sleep until their oath was fulfilled. Because Aragorn wore Andúril and he was the last of the line of Kings of Gondor, the undead were the guys who had to fulfill their oath in order to rest in peace.

As to question 2, altough this is merely an opinion, I think in general Gollum was afraid of people as they called him names while he was in his land and he usually had his revenge by wearing the ring and biting people's toes or something. He was miserable and was so alone that he couldn't leave his home.

Well then that makes more sense, thanks. As for Gollum, I was just asking because he loved the ring so, I was just wondering why if he loved it so, didn't he go after it?

Got some good news. I just heard that someone asked Peter Jackson when we could expect to see The Hobbit and he said in another 3 or 4 years. So, hopefully, by 2009 it'll be out!