Cameron has a 2TB Western Digital hard drive, but his computer isn't able to use it. Leo says that since Cameron had Windows XP, unless he has the Service Packs installed, Windows won't be able to see that much space. He moved to Vista, which should be able to see that however.
It could be that his older hard drive controller won't support that large of a drive. He should check to see if there's an update to BIOS for the motherboard he's using, and check to specs for the controller on the motherboard to see if it can actually handle the larger drive.