The GameCube wasn't Nintendo's biggest success, but the company is looking to change its downward spiral in the console business with the Wii. Speaking to the Japanese press on the 9th, Nintendo president Satoru Iwata said that for the Wii, hardware sales "two to three times that of GameCube is a possibility."
This would put the Wii at between 40 and 60 million units worldwide. Not quite PlayStation numbers, but it's possible that Iwata is just giving a conservative estimate.