w2k server vpn only 1 nic behind router

I have a windows 2000 server that has one nic installed. Internet access provided by a dlink 614+ router

w2k server(one NIC)—>Router(dlink 614+)—>Internet

I need to know how to setup vpn on the w2k server that is behind a router. Putting another NIC card in the server is not an option. Do I have to setup up passthrough on the server?(if so how do I setup this up) Can anyone give me a step by step setup? Can I setup VPN on the server with only one card? (if so How?

Thanks,