I have an Asus laptop (K42JP to be more specific), running Windows 7, that has a combo audio/microphone 3.5mm jack. When I connect either the iPhone's headset or a Nokia headset, I get a pop-up asking the kind of "device" (headphone or microphone). However, no matter which option I pick the headset's microphone never seems to work. Also, in the "Recording" tab of the Sound properties (in the Control Panel) it only shows the laptop's internal microphone.
Both headsets work perfectly when I connect them to a MacBook Pro, so I think it's safe to assume that they are in working order.