** UPDATE: this tutorial explain the 'old' manual way to unlock xbox harddrives. You can now use homebrew xbox apps to easily unlock a drive with 1 button click. ConfigMagic can unlock harddrives, but also newer versions of EvolutionX dashboards and also all 4th generation modchip OS'.
If your Xbox is broken or if for any other reason you want to unlock your Xbox HD on your PC ... you can use this method ... but you will still need the hdd password.
Once a drive is unlocked, you can format and use it in a normal PC **

First of all dl the hdd unlocker here.

Then connect your original hdd to your xbox, using Evox, get your hdd password. (in the evolutionx dash go 'system utils' then 'backup' , this will make a directory called "backup" on the C drive of your xbox. "hddinfo.txt" will contain the HD key)
Once you have it, It looks like this:

01:23:45:67:89:AB:CD:EF
01:23:45:67:89:AB:CD:EF
01:23:45:67:00:00:00:00
00:00:00:00:00:00:00:00

rewrite it as followed:

0123456789ABCDEF0123456789ABCDEF01234567

Yeah delete the last zeroes, and print it out, ull need it.

Now you have to boot DOS (Bootdisk).

Go here for a bootdisk that works with Win98-WinXp.

Once downloaded execute it, enter a Floppy disk in ur computer.
it will make that disk a boot disk.

Then add the files: hdunlock.exe, hdunlock.pas, hddisabl.exe, and hdddisabl.pas to the bootdisk just created.

Now, turn off your computer, set your xbox hdd to SLAVE, install your xbox hdd in your computer.

Turn on your computer with bootdisk inserted, and it will ask you to press a key, then press a key, and you are in A:\>

Type in hdunlock and press enter
Select your xbox hdd, and enter your hdd password

it should say DONE

Type in hddisabl
Select oyur xbox hdd, and enter your xbox hdd password

it should say DONE.

Congratulations you have unlocked your xbox hdd for formatting.

Simple way to format it in WinXP:

Now boot to windows
enter "MMC" in RUN
File-->Add/Remove Snap-in
Click on ADD
New window appears double click on Disk Management
New window, click finish
Click on OK
Click on Disk Management(LOCAL)
then right click on disk 1 and select the first option
now right click on the right box next to the Disk 1 Box
Then click on format, and format it the way you want it, select your partition letter and your ready to go.


Source: xbox-scene.com