how did the sword of gryffindor reach neville?

Well, if you'll remember, Goblins believe that anything made by their hands rightfully belong to them. However, the wizarding world's idea of ownership is the same as our own. Therefore, it's incredibly likely that Godric Gryffindor bewitch the sword to appear out of the sorting hat whenever a worthy Gryffindor needed to wield it. It wouldn't matter who had it in their possession at the time...if a Gryffindor needs it, it would disappear from where it was and re-appear in front of the Gryffindor. Therefore, since Neville had the hat, and was deemed a worthy Gryffindor, the sword appeared to him in the hat. Chances are, somewhere in Rowling's wizarding world, there is one very angry and confused goblin wondering where his sword is. But this is just my speculation, though. I don't know Rowling's explanation of it, but you could always write to her and ask.

Of course it appeared to Neville the same way it appeared to Harry in the chamber of secrets. He was displaying the qualities most fitting for a member of Gryffindor house, so the sword of Gryffindor appeared to assist him just as it did with Harry. Personally, I think Neville is a lot more worthy than Harry anyway...

Neville was able to get the sword, because he had courage and was of the proper house. The sword would appear to anyone of that house, who had courage and was in need of it. The sorting hat was a macigal means to get it to Neville. Remember when Harry used it in the Chamber of Secrets. Doumbledore explained it to Harry then.

Well the sword is a magical object and rightfully belongs to a true Gryffindor, Neville showed in words, deed and spirit that he is a true Gryffindor, that's why the hat was able to give it to him. As for Griphook, I don't think he understand the concept that the sword now belongs to someone else and not to Goblins anymore since they already sold/exchanged it for gold. I think he would be surprised the sword gone from his hand.

How did Neville get the Gryffindor sword, is there a link to the hat? JKR: Yes, there is definitely a link to the hat! Neville, most worthy Gryffindor, asked for help just as Harry did in the Chamber Of Secrets, and Gryffindor's sword was transported into Gryffindor's old hat. -from Bloomsbury Live Chat with JKR