aguimo - 9:05 pm on Apr 2, 2010 (gmt 0)
I don't use Plesk so I'm not sure how much help I can be. Have you read the Plesk manual for what you're trying to accomplish?
If you want to run your own nameservers you need at least 3 IP addresses...
ns1.domain.com = IP address #1
ns2.domain.com = IP address #2
domain.com = IP address #3
You also need to register the nameservers at the domain registrar (not the same as registering a domain name). This should be a free service with instructions at your domain registrar. You can only register nameservers for domains that you own.