Quite a good overview of the effects of computers on your neck, and you're neck's influence over your head and how referred pain can be very painful. Recommend.

An excellent, educational article about cervicogenic headaches. It covers why these headaches occur when using the computer and what can be done to make sure that you can keep future ones at bay. Posture is key here. It also goes into what you can do if you are already suffering from this type of headache due to computer use and poor posture.