GIANTS or NEPHILIM?

KJB Gen 6:4 There were GIANTS in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.

(NIV) The Nephilim were on the earth in those days ...
(ASV) The Nephilim were in the earth in those days ...
(ESV) The Nephilim were on the earth in those days ...
(CEV) ... Nephilim and lived on the earth at that time ...
(NASB)  The Nephilim were on the earth in those days ...
(RSV) The Nephilim were on the earth in those days ...

What is a Nephilim? I thought it was the King James that was supposed to be difficult and archaic? Nephilim is the Hebrew word. Why didn't the modern versions translate it into English so we could understand it?

Addendum 7-14-09:

I subscribe to "Bible and Spade", a biblical archaeology journal. Although they are the most conservative biblical archaeology group I'm aware of, they still appeal to the modern versions and sometimes the Alexandrian texts. The take the position that "Red Sea" was a mistranslation, even in the original Greek quotes of the OT Hebrew.

But they are one of the authorities on Bible events of antiquity. In their current issue (Spring '09) I read an interesting accounting in an article on the Genesis 6 "sons of God" by David Livingston. The authority on antiquity in scripture (and I say that seriously, not sarcastically) has this to say:

{{ "Giants" in verse 4 may mean tall men. }}

Noooooo? You mean the KJB was right all along?

{{ The word niphal [TG: root of Nephilim] refers sometimes in Scripture to men of large stature. }}

You mean like GIANTS?!?!

{{ But it also means "to fall". It may have a double meaning here - tall mean who ... sin grossly. }}

Wow. Sounds just like the GIANTS of Gen 6 in the KJB English.

So after all that scholarship, but textual and archaeological, we come to the realization that the KJB was right in the first place.