Recreating a domain controller

[Chris Starmer]

I am creating a disaster recovery plan for Exchange.

I have two DCs, one of which is running exchange.
WHen that one fails I want to use another machine to
recreate the exchange server.

I need to preserve the name of the original DC within AD
and somehow get my new machine to join the domain under
the same name.

Articles suggest resetting the account with AD, but being
a DC it wont let me.

What procedure should I use to get a machine back on the
domain.

Thanks

Chris