DSL has not matured to the point that you can safely buy a DSL modem from a retail or mail-order reseller. The modem must not only be compatible with your DSL service, but also must be configured properly.

Your best bet is to obtain the DSL modem from your service provider, usually as part of a discounted installation package. Although DSL modems are sold on places like eBay at attractive prices, you should only go that route if you really know what you're doing.

How is DSL installed?

With ADSL, by far the most common form of DSL, you will typically get an installation kit that contains a DSL modem and a number of microfilters:

• DSL modem
  Of the two basic types, external and internal, external is strongly recommended, because it is easier to install and generally avoids driver problems. External modems are further divided into two types of connections to your computer: Ethernet and USB. Although USB is convenient and usually works fairly well, Ethernet tends to be more stable and efficient. USB requires a USB port in your computer, whereas Ethernet requires an Ethernet port.
  
  
• Microfilters
  Microfilters are used to isolate the DSL from your voice telephones (as well as conventional dialup modems, fax machines, and so on). These are small devices that should be installed at each telephone device that connects to the same phone line with DSL. (Instead of microfilters, a single splitter can be installed where the telephone line enters the premises, but a separate dedicated telephone line is required from the splitter to the DSL modem, which can be a hassle.) Performing the installation yourself is relatively straightforward. If something goes wrong, the provider will usually send out a service technician to finish the job.
  
  What is PPPoE?
  
  Many DSL providers now use PPPoE (Point-to-Point Protocol over Ethernet) in order to simplify their provisioning and management of subscribers. The problem for subscribers is that PPPoE usually requires special software that can be difficult to install and configure properly.
  
  For those running Microsoft Windows, an excellent free alternative to special software from the provider is RASPPPOE. Another way to minimize the grief from PPPoE is to obtain a SOHO router with built-in PPPoE support (which has the added benefit of making it easy to share a single DSL service on more than one computer, as described below).
  
  Can I share DSL service on more than one computer?
  
  Although DSL service can be shared with software (Microsoft Internet Connection Sharing, for example), the recommended way to share broadband is to obtain a low-cost SOHO router (such as Linksys BEFSR41), which is essentially a connection-sharing device.
  
  A SOHO router has the additional benefit of providing a protection from Internet crackers by means of NAT (network address translation) and/or firewall functions. (A firewall is designed to block unwanted traffic.) A wealth of information on sharing and networking can be found at Practically Networked.