Well, you could export from the iplanet directory into an LDIF file. Thats all your account information right there. From the from the Sun version of iPlanet (Sun JDS) its right on the first screen that comes up – export to LDIF.
Im assuming its trivial to import an LDIF into open directory (ldapadd probably – thats how you would do it in openldap) from that point. Its just a text file that follows a standard format. Ive never actually done this, but I figured Id answer since nobody else has 🙂