Another solution is to use your computer and assume that you don't use 1.6 Eeprom. I heard liveinfo can't do that or you can use xboxhdm (search for that on this forum). There are better instruction than what I can give you.
Install Liveinfo
Copy the "backup" folder which has the eeprom of the softmoded xbox to your computer
Turn off computer.
Add your new/unlock hd to your computer
Turn on computer and Run Liveinfo and find your eeprom file which you just copied and select the hd you want to lock. It will generate the info you need to lock your hd. Write down the info.
Boot to Dos and use unlockx or hdlock programs to lock them. Tripple check the password/key you entered before pressing enter key. Insert into your softmoded xbox and play. All of those programs can be found on this site under software.