DNS Issues, Zimbra Fedora

I am trying top set-up a Zimbra server on a FC5 box, behind a Linksys Router. I am using dynamic DNS via dyndns.org and have confirmed that the IP updates and that the NS for both A and MX records from mydyndns.og are pointing to my router. I am having tremendous issues with DHCP and nameservers, basically, every time I set-up search and DNS addresses, they revert back to the cable-companies records or the router, and Zimbra cannot resolve the MX record in order to set-up. I have tried multiple configurations and CAN get CNS to work (at least via DIG query), but this is short lived and the etc/resolv.conf gets rewritten within minutes to the cable co's servers and I lose DNS resolution.

And ideas?

Thanks

Put the box on a fixed IP address, and set up the router
to forward the relevant external traffic to that address.
With DHCP disabled on the box, it will no longer dynamically
rewrite resolv.conf