I posted this link in the Planning it Out thread, and then remembered what a fantastic resource it is.
The Paris Review, if you haven't come across it (or even if you have) is one of the great literary magazines. It was started in Paris, in the ex-pat literary spirit of the Shakespeare & Co. bookshop, but is now based in New York. Since the 1950s it has interviewed most of the greats (with a slight but bearable bias towards men and Americans), at length, and in the same question-and-answer format. Since some of the writers were old then, there are insights going back a century or more. The interviews are collected in a series of books by Harvill, but they're all available online here:
http://www.theparisreview.com/literature.php
Quite rightly, it's headed
The DNA of Literature. A couple of these are worth any number of how-to-write-a-bestseller-in-a-weekend books.
Emma
<Added>I've just checked, and they still haven't got the most recent ones online, but you can order that number as a back issue.