I have multiple LANs in different regional offices - different cities.Presently 2 LANs, but expanding.

The typical LAN has broadband service delivered through a Beetel 220BXI ADSL@+ modem (ISP - Airtel). This connects to port 1 of the DLink switch.

Other devices connected to the switch are dual-boot machines (Fedora 9 / Win Vista/XP) as well as network resources such as printers.

How can I connect up these distinct LANs **over the internet** so as to build a WAN - in a cost-effective, speedy/efficient, manageable and reliable way. That will allow me to centralize the backups, maintenance, as well as set up intranet, mail server, etc.

Thanks for any help on this!

Install a router at each location that provides a VPN. Still, your connectivity will obviously be at the mercy of the Internet and your broadband connection.