Pretty sure it's computer specific that they're made.
Yup, under Troubleshooting my my Sources link:
The password reset disk cannot be used to reset the password on another computer.
The password reset disk that you create can only be used with the computer it was created on. For example, if you have two Windows XP-based computers that have the same user names and passwords, a password reset disk that you create on the first computer cannot be used to reset the password on the second computer.