OPENVPN

I have subscribed with a company called vpn4voip to run my voip termination business but I need to setup this on my own servers. They provide me service as follow: Before each voip gateway ( e1 with 32 ports ) they ask me to get a computer with 2 network cards one of the network cards is connected to wan and the other is connected to my gateway and they bridge the 2 connections somehow and give me public ip address on their server in USA to assign to my gateway here so I have all my voip traffic to gateway tunneled and avoid ISP blockage. NOW I want to know what is needed from me on the server side to setup this solution (if any). I have windows 2003 server in USA dual xeon with 2gb ram and subnet is .248 IN BRIEF If you are one my clients in usa and want to call india you will call this ip for example x.x.175.1 ( which is one of the ip addresses on my server in usa ( my server ip is x.x.175.74) ) and when you call this ip you will reach my server in usa which intrun will router your call through the vpn tunnel to the gateway here in india we assigned this ip to it. I will need your help to setup 2 gateways to understand the concept and then I will do the rest myself. What will I need on the server side ( pc specs and os ) This is the network scenario with vpn4voip [login to view URL] Happy biding