Just how different are the Jewish texts and the "Old Testament"?
Well, the Jewish Bible is the Tanakh, which is an acronym (the T stands for Torah, the N for Nevi'im or Prophets, and the K for Ketuvim or writings) and the Tanakh is assembled in that order. Thus, the Jewish Tanakh has a different order of its books than a Protestant New Testament (and, as the poster above me mentioned, the Catholic Old Testament has a number of books that aren't in either the Jewish or Protestant Old Testament). The main difference between a Jewish Tanakh and a Protestant Old Testament is the ordering of the books and that there's a general idea that the Torah is more important than everything else in the canon.
That said, Jewish canon doesn't end with the scripture itself, and the thousands-year old commentaries on commentaries on commentaries has a sort of secondary canonical power itself. The first layer is the Mishnah, which is a compilation of rabbinic commentary and interpretation from ~100 BCE to ~200 CE. The Gemara, a set of discussions on the Mishnah written between ~200 CE, to 500 CE, is the next level down. The Mishnah and the Gemara are together known as the Talmud, a document about 5 times as long as the Tanakh itself.
In addition, there are various non-canonical but elucidating rabbinical myths called the Midrash that serve to explain various Bible stories. The Book of Exodus says that Moses has a speech impediment? The Rabbis invented a Midrash explaining why he did: young Moses, in his Prince of Egypt days, was offered a choice between grabbing a golden idol or a bundle of burning coal. He touched the coal instead of the idol, then, as children do, touched it to his mouth, burning his tongue. The Midrash are explicitly non-canonical but the better ones are quite famous and are treated as semi-canonical anyway.
