duplicating a disk

[cfk]

Gentlemen:
 
 I have a situation where I need to make a number of identical computers all 
with the same fedoraCore2.

 I have tried putting a second (hdb) disk, doing a "df" on hda and based on 
the number of 1024 blocks going:

dd if=/dev/hda of=/dev/hdb bs=1024 count=<TheNumberDfShows>

and it blinks the light a long time and then croaks.

 I know I did something similar to this a couple of years ago on a different 
project. Can someone tell me where I am going awry and perhaps educate me a 
little bit more.

Signed, OldDogTryingToRememberNewTrick