I found this story at scifi.com . It's only a rumor, so take it with a grain of salt.
Is Pixar Mulling Live-Action Mars?
The Disney insider news site JimHillMedia reported a rumor that Pixar's first foray into live-action filmmaking may be a film based on Edgar Rice Burroughs' John Carter of Mars series.
Citing anonymous sources, the site reported that WALL•E director Andrew Stanton told the staff at Edgar Rice Burroughs Inc. in October of last year that Disney/Pixar is gearing up to do a trilogy of films based on the books.
Mark Andrews has reportedly completed a first pass on a screenplay for the first film in the series, to which both Pixar and Disney executives have responded enthusiastically. Both companies are reportedly eager to put the project in the development pipeline soon, with an eye to a 2012 release, if not earlier.