I have 120Gb HDD in my X Box :).

When I put my 10Gb HDD in (from another X Box but loaded with slayer etc (I have used it before in my X Box I think) I get an error message.

Why is this? Is there anything I can do about it as i am trying to unlock it to go in the PC!

Thanks in advance.

The HDD is 'locked' to the Xbox it came from - you can't unlock it using another Xbox because the info you need is in the original Xbox eeprom.

The HD is useless, unless you got the original xbox where the HD came from. Or you know the HD eeprom number so you can edit in ConfigMagic.

If the HD is unlocked from the original xbox, will it work on any other xbox?

Yep, so long as it's unlocked.