The question I have is: Why???
Gatsby is already in the public domain in his home country of Australia, Canada and other territories that use a "life, plus 50 years" copyright term.
For most other countries (including the U.S. and most of Europe), Gatsby becomes public domain in just over a year from now. Fitzgerald died in 1940. Applying the (insanely long) term of "life, plus 70 years", "Gatsby" should fall into public domain sometime in 2010.
[Am I wrong on this? I've double-checked my math and the current state of copyright law, so I don't think I am.]
Since it usually takes over a year to develop and produce a major Hollywood film, Luhrmann's adaptation of Gatsby wouldn't be released until after the original literary work falls into the public domain worldwide. Clearly it doesn't violate copyright laws to merely begin production on an adaptive work that won't actually be completed until after the public domain date. Any unpublished drafts of potential scripts and other developmental materials would certainly fall under fair use in this instance.
Luhrmann wasted his money. But then, Hollywood culture has always been overlawyered when it comes to IP rights.
For anyone who wants to make their own "Gatsby" adaptations to compete with Luhrmann and release it around the same time - have at it! May the best quality work garner the most attention. Hopefully, the competition will raise the quality of all works involved.
[UPDATE: As Gilda Radner used to say: "Never mind. As someone who follows copyright law, I'm admittedly embarrassed in that I forgot that the "life, plus 70 rule" in the U.S. only applies to works published after 1977. Gatsby was published between 1923 and 1963, so it remains under copyright in this country for 95 years (since the copyright was presumably renewed). So Gatsby won't become public domain in the U.S. until around 2020. But the anomaly still stands that it is public domain in countries such as Canada and Australia.