Virtual Private Networking

I am in need of assistance with configuring a VPN. I am running NT Server 4 (svc. pak 6a), Proxy Server 2.0(svc pak 1), and Routing and Remote Access Svc. I have a cable ISP. When connecting the remote network, or when the remote network attempts tolog into my network, i get “Authenticating User” and then it eventually times out. Please advise if you can help, or know where I can find help. The MS website hasn’t really helped me. Thanks.