GnuPG can import keys generated with versions of PGP. The HOWTO is documented in <http://www.gnupg.org/>, and commented in various mailing lists.
GPG Keychain Access
GnuPG key management
Version: 0.7.0
Existing users, log in. New users, create a free account. Lost password?
GnuPG key management
Version: 0.7.0
No user comments.