calling the Hebrew-literate

A friend asked me about the word "n'filim" (or sometimes "nefilim"), which is the noun for the giants talked about in Gen 6:4 and Num 13:33. Or is it? ORT asserts that the former is literally "fallen angels", but armed with a dictionary, 501 Hebrew Verbs, and the knowledge that "angel" is usually a completely different word, I'm not seeing it. Oh, and there's a slight difference in the Hebrew in the two places cited, a small matter of an extra yud, and I don't know if that's a root change or some grammatical transformation.

The discussion is here (and specifically here). We'd welcome further clues from you folks who know a lot more of this language than I do. :-)