Transfer an account from a 'dead' domain

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http://serverfault.com – So - following from my previous question: How do I stop DFSR replication preventing a Domain Controller from advertising Domain Services?, I lost the FSMO DC, and my only other DC was in an unrecoverable state. I've created a new domain to continue my testing, but now have an issue which I suspect is relevant to any domain suffering a "catastrophe". I have user accounts and client PCs "on the old domain". (Actually 1 client PC and 3 accounts) I can still sign into the client PC as any of those users on the "dead" domain, because that is cached. There are (thankfully) no encrypted files in (HowTos)