[Orin]

XBOX hard drive is "locked". It has to be unlocked first by removing/disabling the security. You have to hot swap it. Turn on XBOX(let it boot to menu), remove IDE cable(NOT power cable, leave that in so it stays on) and hook it up to your PC. You should be able to access the hard drive then but you will need to disable the security on it so when you turn of the hard drive, it does not lock itself. (i had a program around here somewhere that i used to do it with both my little bros XBOXs that i said was "broken". i'll look for that.)
After you unlock it, you will not be able to use it in the XBOX again. i'd only do this if an XBOX is broken like DVD drive doesn't read anymore so i can gain another Hard drive.

Edit:
I attached ATA Security Tool. Add atawd.exe in the .zip to a MS-DOS boot disc(floppy if ya got one lol). Do the hot swap and then boot from floppy and run atawd. once in that, you can disable the security so it will always be unlocked.