According to a post on KyleHebert.com (personal website of VA who voices teen Gohan in the DBZ anime), 20th Century Fox has abandoned plans to produce a live-action film adaptation to the Dragon Ball Z anime series.
If true, this isn't surprising, considering it's been well over a year since Fox originally announced the project, and yet there's been no solid details on the cast, the script or even a director. That said, there is a chance that this information could be false. So until Fox issues an official statement regarding this, nothing's for certain.