The info is on this site.
The pictures in his link show you the drive, its pretty straight forward as far as I know. But the word on the street is it has to be a scorpio. The OS is not held on the HD.
But I think the reason nobody is rushing about changing hard drives, is external drives are cheaper, bigger and you dont void your warranty. Plus copying stuff onto the internal 1TB drive takes a lifetime, only a madman would want a 2TB internal.