Domain Authentication via VPN

Currently i have two networks:

Location 1: (connected to internet via dsl router)
-Anubis is the domain controller
-Cynic is a client that moves to both locations
-Thor is a client that moves to both locations
-there is also two other computers (not part of the domain)

Location 2: (connected to internet via dsl router)
-Cynic (is here or at location 1)
-Thor (is here or at location 1)
-Another computer not part of the domain

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My main problem is the user that Thor belongs to is pretty computer illiterate and really dislikes any changes is steps or appearance.

I would like to setup a vpn so that Cynic or Thor can authenicate via Anubis when they are at location 1 or roaming. This would remove the need for multiple logins/profile.

Is is possible to make this seamless?

I was messing around with VPN's a few years ago, and couldn't get it working right. I was trying to log on as admin for a W2K server. The problem was the router, on both ends. Now, i think it would be possible, as we both have different routers.
You can supply an IP address for each connection for each person. Have them type in username/password, or have one or both supplied automatically.
It should be easy.

I cant get the server to accept a connection from a computer outside of the internal network. it works fine if im on a computer in the local network and use a private ip but if i use the public ip (even in the internal network) it refuses to connect. (i even configured the server as the DMZ zone in the router)

you have to open the port, if a firewall is involved.

Server is in the DMZ zone.

Firewall rule:

Source: WAN,*
Destination: LAN,192.168.2.1 (server address)
Protocol: *

Edit: ICF disabled too, Windows 2003 Server Enterprise :D

I'm not sure about that. Sorry.