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First of all, you'll have to check if your Internet connection runs on IPv4 only. If you get an IPv6 address, VPN won't work that well.
Information on how to set up the VPN on the Internet Box can be found here.
From what I can tell, the VPN is based on L2TP over IPsec and uses IKEv1. On a Windows client, you might need to edit the registry to make it work.