When you say they 'don't work', you mean no sound in the headphones and no input detected by the computer from the mike? If you play sounds/music on the laptop, does the audio come from the built-in speakers?
You might have to set the audio in/out devices explicitly for this headset. With the headset plugged in, go into System Prefs->Sound, choose the Output tab, and make sure the headset is listed on the output device list. Select it if it's not already selected, and see if the audio comes through the headset now. If the device list just says, 'Internal Speakers', then it hasn't detected the headset as an audio output device and you may have driver problems, as the other poster suggests.
You can do the same for the Input tab - make sure the headset is listed as an input device and select it for input if it's not already. If only the internal mike and line-in port are listed, then the OS hasn't detected the headset mike as an audio input device and again, you may have driver problems.