Looking at the photos from ifixit.com.
The difference between 80 gb to 160 gb thickness is 3 mm!!! I know it is going from 5 mm to 8 mm, which is a big percentage change, but we're talking about 3 mm. There looks to be enough foam on the surface of the drive to take up at least 3 mm.
So I figure, you may be able to stick a 160 gb 8 mm drive, lose some foam protection and then enough room for most people.
The difference between 80 gb to 160 gb thickness is 3 mm!!! I know it is going from 5 mm to 8 mm, which is a big percentage change, but we're talking about 3 mm. There looks to be enough foam on the surface of the drive to take up at least 3 mm.
So I figure, you may be able to stick a 160 gb 8 mm drive, lose some foam protection and then enough room for most people.