When calling into an ISP that supports PPTP, all of the VPN work is done for you by the ISP on their remote access switch. You just have to configure your client as if you’re dialing directly into your RAS server; the ISP’s switch will pass all the authentication information to that RAS server.
When dialing into an ISP that doesn’t support PPTP, you’ll need to initiate a PPP call to the ISP using the Dial-Up Networking dialog box. Once the call has been connected, leave your PPP session up, select the PPTP entry you made (in our case, it’s called Central Office VPN), and click the Dial button. This will initiate the PPTP call to the corporate RAS server over your PPP Internet connection.