dd does not care about file extensions, it's a beast, it will start at 0 and continue until the file is written.

here is how i use DD to make a complete copy of the Sco Unix server HD at work

open terminal in mac

- type

- diskutil list

- now you see the 40 gb drive, /dev/disk0 or something like that

- type: sudo su

- dd bs=1m if=/dev/disk0 of=unix.image

- this will take some time you can follow the status of this by typing in ls -l

it will show you the size of unix.image, when it gets to 40 gb wala!

- now, unmount the 40 gig drive

- connect the new IDE drive, in my case it was a western digital blue 320gig 32mb cache

- diskutil list - just to make sure the device has not changed numbers

- dd bs=1m if=unix.image of=/dev/disk0

- you can now open up activity monitor, and click on disk activity and when it counts up to 40gig written +/- it will be complete.