Yep.
You need to use Router Advertisements to do this. The following was used in Vista, but the steps should be really close for 2003 server. You'll obviously need to substitute your IP addresses where needed.
Steps to configure host to act as IPv6 router
1. In CMD type: netsh int ipv6 set interface IP6Tunnel forwarding=enabled
2. Next, type: netsh int ipv6 set interface "Local Area Connection" forwarding=enabled advertise=enabled
3. Next, add the first address of the routed IP address to the Local Area Connection
netsh int ipv6 add address "Local Area Connection" 2001:470:8:a0a::1
4. Next, add the default route and next hop for the tunnel and Local Area Connection, then publish it:
netsh int ipv6 set route 2001:470:8:a0a::/64 "Local Area Connection" publish=yes
5. Next, add the default route for the tunnel and publish it:
netsh interface ipv6 set route ::/0 IP6Tunnel 2001:470:7: