[Orin]

You put a floppy in you floppy drive and got o My computer and right click on A:\ and format, check Create MS-DOS startup disk. Once thats done, copy atapwd.exe to the a:\ And about the unlocking, The key for this working is hot swaping as the XBOX already unlocked the hard drive but you have to use that program to change the key/password(whatever its called). Like select drive, security options and set master password(this changes the code that is needed to unlock the drive, i set mine to 'password' easy to remember) Then select unlock with master password and enter the password you set for master. Then you can go from there(like unlock or disable, disable i think means it disables the security on the drive so it runs just like a normal PC hard drive.)
It is possible to use a XBOX hard drive in PC doing this. I'm using my old XBOX hard drive in my cheap server right now and the xbox it came from was not modded. However once you unlock it for PC use, you cannot use it in your XBOX again as it will not boot(plus you have to reformat the drive).