Hello Hybrid,
When you connect, use your own DNS server so that you can surf. In order to join the domain however, your machines will need to know the FQDN of the server. A little workaround that you can do it to add the domain name and the server's FQDN to the hosts and lmhosts file on your PC's. This way they will be able to resolve the remote server's IP address even though it's not in the DNS tables.
Of course this is just and idea to go from, there is not enough information here for a better solution. If you can enumerate your topology a little bit better it would be helpful. Is your IP sec VPN using a router to router network? If not what client software are you using? When you ping the remote servers are you pinging using the natted address, public address or can you ping using the host name and FQDN?
Miguel
Miguel Fra www.falconits.com