i am planning to setup ip sec vpn tunnels between two remote offices however ill be using dydns.org as my dns/host provider,I believe that gradually,the public ip address changes and i believe that theres a script to refresh or update dns everytime the ip changes,something like every 5 minutes, can anyone tell me thaty script and how can I load in on routeros,thanks

You can't update DynDNS with Mikrotik as it's not the standard DNS update protocol. ChangeIP.com offers a free dynamic DNS service that does work with Mikrotik here:
http://wiki.mikrotik.com/wiki/Dynamic_D ... angeIP.com