I'm affraid this project had been cancelled in 2003. In that time, there was someone else working on an other adaption of the biography of Hughes.
From Imdb.com:
Following Insomnia, his next project was going to be a Howard Hughes biopic starring Jim Carrey. Nolan had the screenplay written (calling it "one of the best things I've ever written"), but once it became apparent Martin Scorsese was making his own Hughes biopic The Aviator (2004), Nolan reluctantly tabled his script and took up directing Batman Begins (2005).