how to encrypt the windows product key in sysprep.inf?

Hello,
Does anyone know how to encrypt the product ID in the sysprep.inf for WinXP
or Win2K3? I know microsoft has a way but it's time sensitive. I need find
a way to prevent someone from restoring the sysprep image, then mounting the
disc somewhere and find the product key in the plain text sysprep.inf file.

Thanks.