Here is a Microsoft technet suggestion for backing up the DHCP server.
And here is how to roll the DHCP information to another Server 2003.
But just make sure you keep doing your backups daily at least and test them every once in a while and make sure they are actually working. You can always have a backup system to load the DHCP information on to roll out in a emergency. But otherwise an external backup solution that can restore the machine in a couple hours is about as good as you can do.
See my blog entry: Using net shell to backup/restore DHCP. Let us know how it goes!