Have you had the required users create the VPN connection by going to
Network and Dialup Connections and select Create New Connection, then
selecting Connecto Private Network via LAN (assuming broadband on LAN) or
Dialup Connection to Private Network (assuming modem connection via POTS)?
This piece will need to be configured, where they will be asked for the
connection parameters to your VPN server (IP, etc) and authentication will
take place when they connect to the VPN server.