The Mac OS X Server Open Directory Administration Guide for Version 10.3 and Later provides instructions for backing up and restoring Open Directory files. Do not use this guide when migrating to Mac OS X Server version 10.4.
The reason is that the LDAP schemas are different in 10.3 and 10.4, so you can't use 10.3 backups to restore 10.4.
Instead, you should follow the instructions found in Mac OS X Server Upgrading and Migrating For Version 10.4 or Later to recreate Open Directory data when migrating from version 10.3 to version 10.4.