Syl20 wrote:
> I have open an account with dyndns. I guess what I need is a
> secondary dns service...
Consider Granitecanyon. They provide DNS services for free.
http://soa.granitecanyon.com/ - to make them a secondary, you have to list them in your domains 'whois' records (who did you registrer the domain name with?) as being responsible for your DNS. Usually there are options to list several DNS servers for your domain. You would include NS3.GRANITECANYON.COM as a backup nameserver once you had gone through the granite canyon setup procedure.
> But where do I point the main IP for the domain?
Does this domain live on your SME server? If so, your DNS records would list your SME server's IP address in all fields. A, MX, etc.