Some Windows laptops have one audio input that can switch between two different services -- Microphone and Line.
You need to go into the laptop hardware services to figure out what to do. Some of these services allow you to change the hardware in the Windows control panel.
Line-In typically is high level, stereo and takes a Tip/Ring/Sleeve connector (one ring). The headphone out of an iPod is line level as is the audio output of most CD, DVD, and Cassette players.
Mic-In is very low level mono, but still takes a TRS connector with a variation.http://www.kozco.com/tech/audioconnecto ... ctors.html
Mic-In connections typically have software arrangements where the one microphone appears on both left and right. Some just give you mono and have a happy day. These connections were designed for a communications system like Vonage or Skype. Most communications headsets will plug straightaway into a Windows machine.
Macs don't work that way.
You know immediately if you get the wrong one because you either get no sound or hideously distorted sound. In rare cases you can damage the computer by picking the wrong one. Start the computer expecting Stereo Line-In. That's harder to break.
<<<Shure's site that most laptops have a line input>>>
Most Windows Laptops have a Mic-In. Macs have Stereo Line-In. Most Windows Deskside machines have both.
We use the thousand to one rule. Microphones generally are a thousand times quieter than line connections. There are hot microphones out there and low level Lines, but that's good to go on. The problem with trying to hit it in the middle is the microphone. Microphone level is roughly the same level as noise generated by electronics. You can't mess around much without killing the microphone quality.