W2K VPN Workgroup Server

I have a W2K Advanced Server with one NIC and a static IP connected to a Workgroup. A Flowpoint 2200 router provides Internet access and DHCP service for the LAN. According to the ISP, they configure a port on the router that forwards VPN traffic to the W2K server. The remote clients are getting error 650. I have created user names on the W2K server for remote use. I have followed article Q308208 How To: Install and COnfigure a VPN Server and Q254316 Create a RAS server for a W2K-Based Server in a Workgroup. Both of these articles want to use a connection device other than the NIC in the server. Can I configure the one NIC to be the internet/external connection device?

George
gjjew@yahoo.com