The King James has seven less books than the Catholic Bible because the protestants threw them out during the "reformation." Also, the KJV is translated within a certain dogmatic understanding.
The Gideon bibles in hotel rooms are also Protestant, missing those same seven books, and translated within a certain dogma.
Translation is tough. The oldest versions of NT writings we have are all in Hellenistic Greek, which is essentially a dead language and has no punctuation or capitalization at all. Except for Luke and Acts (written by Luke, the Greek doctor/historian) there is no reason to assume that any of the orginal works were written in Greek. Matthew was probably written in Hebrew. Mark, John, all of John's and Peter's epistles were surely written in Aramaic. Paul could have written in Greek but may have used Hebrew or maybe even the language of the people he was writing to.
The Catholic Church is the one that preserved all these writings and eventually translated them to Latin, the most universal language in the world at the time, and divided them into verses and sentences. This is not a perfect science, to be sure. I studied Hellenistic Greek in college so I could "read the NT in the oldest version possible." But it wasn't anything like I expected. One word might have six different meanings, and a lot depends on the syntax, the context, the conjugation, etc., plus one has to consider that any colloquialisms of the day may have been lost -- and the only way of knowing that is to read volumes and volumes and volumes of writings from the same time period until you have a "conversational" understanding of the language.
Anyhoo, that's why it's so easy for a group of people who have one understanding of things to come up with a translation that supports their views -- whether or not that's what the writer actually meant.
The difference between the Old Testament and the New is that all the OT books were written before Jesus came and all the NT ones were written after His Crucifixion, Resurrection and Ascension.
P.S. Sadie above is completely mistaken when she says the Catholics threw out the second commandment. That's a complete lie, and if she would have ever bothered to crack open a Catholic bible, she would see that "the graven images" part is in there. She also seems to fail to understand that the 10 commandments are not numbered in either her bible or ours -- the numbering is just a convenient way to memorize the rules. We Catholics put "I am the Lord thy God, Thou shalt have no other gods before me, and Thou shalt not create graven images" all together because they run to one theme, while we divide "Thou shalt not covet thy neighbor's wife" and "Thou shalt not covet thy neighbor's property" into the 9th & 10th because those are very different types of coveting. Protestants like Sadie divide "I am the Lord" and "No graven images" into the first and second and group the two different types of coveting into the tenth, but Scripture doesn't say either way is correct or incorrect.