The adaption which they have apparently agreed with the Tolkien estate (and who will have an editorial veto on any non-authorial story lines that they do not approve of) will cover the period of the rise of Sauron following the defeat of the original top baddie (of whom Sauron was a mere lackey in The Silmarillion) to his defeat in the battle which we see at the beginning of Jackson's TLOTR films. This era known I believe as the Second Era, is covered in works of the maestro that sit outside his magnum opus, though which ones I could not say.
The makers are certainly not rushing the story though - the first series is set to have twenty episodes by all accounts, with a second of equal size to follow. The production has apparently cost four hundred million dollars to buy the rights to make and goodness knows how much more to actually produce, so it's a big gamble for the company, but hey - no risk, no win.
Should be interesting - hope they don't louse it up. Tolkien deserves only the best.
