Secure Network

Hi
Not sure if this is the right forum but I have been tasked with designing a secure network for a company that has offices scattered around the country and a headquarters located abroad where the servers are also located. Each section has a local network that is connected through the public network. They require that all desktops at these locations can access the servers.
There are some design goals to meet these are:
1) passwords never be sent across the unsafe network
2) communication between each site must be encrypted (each IP packet)
3) Only one IP address at each location
To meet the requirements I have made the decision to use Kerberos, IPSec, Firewalls and NAT however I am at the design process and not sure if my diagram is correct and that I have chosen the security methods that do the job required is there anybody here that could advise me?
My design can be found here: https://docs.google.com/open?id=0B6...c3hKN1FqWGFKM28
Thanks

Do you mean a VPN ?

Yes pretty much. Just want to know if the technologies I chosen will do the jobs I require and if the rough diagram I came up with places them in the correct order