I'm trying to use a headset over skype to chat while I'm playing games online. The problem is that I have a headset that plugs into a microphone and headphone port, and apparently my intel iMac doesn't have one. It just has a line in port and an headphone port. The built in mic works but it picks up all kinds of background noise. I checked my macbook pro and saw that it also had a line-in port but no microphone port. Same with my friends MacBook. In sound settings in system preferences, I don't get any audio input from my headset. What can I do?