I just bought a new microphone, and plugged it into the back of my Mac Mini. I can't seem to get it to work. I went to System Preferences > Sound > Input, and the only device I see listed is "line in." This isn't the microphone, is it? Nothing I do seems to make it work. Any suggestions?
The Mac Mini's line-in port is a line-level input. That means it's not providing any power to the device, so an unpowered computer mic is not going to work. You need something to pull the mic-level input of the mic up to line-level, like a mixer or certain types of powered mics.
Alternatively, you can use something like the iMic, or any USB mic/headset from Logitech, etc. If your Mac Mini is a model with Bluetooth support, you could also use a Bluetooth mic.