If you're having trouble setting the nameserver records, please contact online.net support.
You will need to update the name servers as below:
NS1.WORDPRESS.COM
NS2.WORDPRESS.COM
NS3.WORDPRESS.COM
For more information, please visit the help documentation provided by the registrar and our support page:
http://en.support.wordpress.com/domain-mapping/map-existing-domain/
Let us know if you have any questions!
