Hi there mate,
Best way that I use is to leave the original hard drive in the xbox, do the softmod that gets evox or whatever on to the xbox. Now configue your xbox to be able to connect to your pc via LAN.
Next copy config magic to E:APPS\ on the xbox using an ftp program, smartFTP is good.
Now shutdown your xbox, whip the cover off and boot the xbox up again, run config magic from the file manager in evox and then when it gets to the bit with the warning about damaging your xbox, disconnect the power and IDE cables from the xbox hdd and resting your new hdd on top of the xbox, plug it in [lay a piece of plastic or a magazine between the new hdd and the xbox] .
Now press start and the HDD UNLOCK CODE [the big text at the bottom of the screen] will be the code that you need to use to lock that particular drive. If you like test it out by running config magic with the original xbox hdd and the unlock code will be different, thats what they don't tell you!!
The unlock code is not the same as the cipher that is used to generate the code and I think people get confused between the two. The unlock code is derived from both the cipher and the hdd id, so no two drives in any xbox, even the same xbox use the same lock/unlock code.
All I then do is run the old "make me an xbox hard drive linux util" with my pc but do not bother with the old "lock it for me" stuff. After the drive has been prepaired I simply use a dos based manual lock/unlock utility, xbox-scene will have something in the download section.
The most important part is: TRIPLE CHECK THE CODE THAT YOU ENTER TO LOCK THE DRIVE - ONE DIGIT WRONG AND YOU'VE JUST LOST AN EXPENSIVE HDD AS YOU WON'T KNOW WHICH DIGIT OF THE 40 YOU GOT WRONG!!!