It wouldn't work. The hairstyles alone are iconic. What? Have actors running around with wigs on? Not to mention how the heck they'd pull Piccolo off. I'd love for a decent DBZ live action film, but come on... if it could be done (And done well), Japan would have been all over it by now. But DBZ is one of those Manga were it's success is partly due to Toriyama's art style. Same with Oda and One Piece.
There is a reason most anime/manga live adaptations fail: they rarely can capture the feel and look of those works. Only a few made in Japan have ever been successful.