Passwording or hiding a file on CD

I want to be able to put some files on a CD that would only be available or visible to someone with authorisation. The CD could be used on both NT and Solaris machines, and therefore just setting permissions on the file wont work because in unix root can see all.
Its been suggested using something like WinZip or tar to bundle up the files and password-protect the resulting file, but we cant find anything that protects on both platforms.
Any ideas?

Thanks
Jo