D'oh, good thinking. I'm apparently on a one track OSS mind right now. Copyright's an excellent reason :-)

Looking at http://cpan.org/SITES.HTML, I found this:

Private/Local Mirroring If you want to configure a private/local mirror of CPAN but do not want to advertise it you do not need to contact the CPAN admistrators. You need to assess which of the public CPAN sites would give the best ftp bandwidth for you (at off-peak hours) and contact the mirror admin via the email address given in the MIRRORED.BY file to learn the best time of the day to do your mirror. Mirroring software is available from the CPAN or from the Mirror home page which will have the most recent version. We also encourage the use of rsync. We encourage you to read our FAQ Section on how to mirror CPAN and visit the mirror database to find a mirror close to you and to register yours with CPAN.

It points you to the FAQ Section on how to mirror, which was going to be my next step as well :-)

UPDATE: Looks like cog beat me to it, with better information. CPAN::Mini looks pretty fun, and simple to use. I'd start there as cog suggested.