See also: ClearOS on a laptop
If you are lacking a network card, you can always add via USB. For example,
Any network card that works on CentOS will almost certainly work on ClearOS as well. Please share your experiences below. These can be ordered online for a reasonable price but they don't always work with ClearOS. Since it can be a hit & miss, you may want to order a few from different vendors, to increase the odds that you will have at least one that works. Search for “usb rj45 linux” at your favorite store ex.: Ebay.
A built-in network card will very likely be more reliable than a USB network card. Thus, use this one to connect your modem (Internet connection). More things can go wrong with your Internet connection so if it doesn't work, you won't easily know if it's ClearOS (a software issue), a DSL issue, a DNS issue, a USB issue, an unplugged USB cable or an issue with the USB network card.