2003 standard VPN server requires two NICs
For the security reason, 2003 standard VPN server requires at lease two NICs. If you have just one NIC on the server, you may receive following message while configuring VPN on 2003 server: "Less than two network interfaces were detected on this machine. For standard VPN server configuration at lease two network interfaces need to be installed. Please use the custom configuration path instead.".
If you would like to setup VPN with one NIC on 2003, you may select the Custom Configuration.
Networking, VPN, TS, Remote Access and Internet Troubleshooting