Many client systems now come with integrated NICs on their motherboards. Often, however, this NIC fails, and that can be difficult to diagnose. If your NIC fails, then unless you have defined a local account you might not be able to log onto your system. Failure can be not only a hardware issue, but a driver issue also. Given that the price of Ethernet NICs has come down substantially over the past couple of years, it makes good sense to add a PCI NIC card to your client systems. That gives you an alternative connection method.
Having an add-in card for your primary client connection has some additional advantages. You can standardize the model and manufacturer of your add-in NIC cards thus making it easier to provide driver support and replacements. While there are many manufacturers of Ethernet cards, and generic cards can be had cheaply, it's probably a good idea to favor the use of brand name manufacturers like Netgear, 3COM, Intel and others. They tend to get better and longer support, especially for driver development.
A secondary reason for going with a second NIC card as your client connection arises with Windows XP. Your NIC card is one of your primary identifiers of your computer's validation for the operating system. You are less likely to trigger a request for re-authenticating Windows from Microsoft when one of your identifiers is a NIC card that is off the motherboard.
Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.