If I get a webcam for my Mac mini, will I be able to use its built in microphone for audio chats in iChat? It is a UVC camera so it should be supported for video, if that matters for the situation.
Yes, iChat - and really any other audio app can just be set to use a webcams built-in mic as a USB audio input source. It'd really recommend SoundMenu which is a great menu bar utility for easy access to in and out-put sources.
If you haven't gotten a UVC web camera yet, check for some good choices at this Mac Compatible Webcam site. Most midrange - and all high-end cameras include a mic. Avoid something like the low-end crappy MacAlly IceCam2 - not only is its image lousy, but it's microphone is just NASTY and HARSH sounding.
You could also try to track down an original iSight Firewire camera. Excellent noise-canceling microphones built-in, everything runs off of Firewire 400.