Godaddy extra domain nameservers

I’m having problems setting up an extra domain with Godaddy. I’ve seen a post about this problem, but my box nameservers have been registered for a long time, and it says “use a registered nameserver” when I try to enter the ns1 and ns2. Tech support says they have to point to two different IPs, when I only have one as most people do. The tech support guy didn’t say anything about registering them or anything, and they show up as authoritative NS’s when I look up my other “secondary” domains.