OpenDirectory Passwords

I'd like to preface by saying I'm a Unix Administrator but have had almost zero experience with Macs in the past 10 years. Sooo, if you put it in Unix Terms I'll understand, the Mac Jargon I won't get.

Trying to help some family members that recently picked up an iMac from the local School District that was upgrading it's computers. It's running OS 10.5 (Leopard?)

There's three logins when allowing a regular boot, Admin, Teacher, & Student.

We don't have the OS install disc or the Admin passwords.

Booting to single user mode, the /etc/passwd file didn't have any of those three accounts and a passwd command was unable to change them. It appears the school had been using OpenDirectory (Mac LDAP implementation if I'm understanding this properly). Since we're not on the school network anymore, can't change the password or talk with the LDAP server.

My questions would be:

How can I get the machine to quit trying to use LDAP and only look to local accounts?

Is this thinking wrong? Perhaps Macs have a second place that stores local login info?

The machine was legally purchased without discs or documentation, is there a way to get a copy of the OS X disc?

suggestions? *polite bump*

You could try going into an Apple store and ask them to put the original operating system back on. If they do, you would get the iMac as though it was fresh from the box, creating your own original Admin user at first boot.

The other option would be to find out which model iMac you have and match it to disks people are selling on ebay.