Registering your domain name with Yahoo isn't too complex. However, it does require a little more work, then normal. Please follow the below link with more information on how this is done:

Yahoo DNS Name Servers

1. Ask them to register your name servers in this format:

   NS1.YOURDOMAIN.COM | IP: 123.123.123.123
   NS2.YOURDOMAIN.COM | IP: 123.123.123.124

2. Please remember to change the "123.123.123.123/124" with the IP addresses that you have been assigned in your welcome email when your received it.

If you have any further questions, please contact support by opening a support ticket.