Ask HN: How to produce quality video of tech talks + lectures?

I've been consuming a lot of good YouTube videos on software development lately, mostly from conferences or tech talks with big audiences, and I'd like to try producing videos of my own lectures (and guest speakers) in the classroom that's up to par. Typically the best videos show the speaker as well as a capture of his screen (typically switching back and forth between the two). But I don't know anything about A/V stuff. What's the best way to cheaply and simply create videos like this? I'd like to start as inexpensive as possible and iterate before going for expensive equipment.

Sub-questions: (1) What kind of camera? (2) What kind of audio equipment, microphone, etc? (3) How to capture screencasts on my own (Linux) and guest (Win/Mac) computers? (4) How to edit? How to capture audio/video in a way that doesn't make it too difficult to edit?