This has been a problem with Linksys routers for as long as I can remember, would have thought they would have either sorted the problem or removed support for the dyndns.com service.
I cannot see how you can do this, how will your server, sat behind a Linksys router, know when your public ip address has changed?
Have you thought about going the easy route and setting your SMEserver up in server+gateway mode.
Dave