What's involved? First of all, I need to record what I see on the screen, which I do using FRAPS -- you can get a free version which lets you record up to 30 seconds of video at time, so I just do everything in 30 second chunks! That produces a bunch of 'AVI' files, which I then load into Windows Movie Maker, which I use to stick them together, with simple intro and ending title screens.
Still in Movie Maker, I record the narration to go with the video. That usually takes a number of attempts, and I've found it's useful to ad lib it a few times to get a feel for the timing, then write down the script, and then record it for real. Different approaches work for different people I guess.
Next comes the music, which I typically get from the wonderful SoundSnap website. Unfortunately, Movie Maker doesn't seem to be able to mix audio tracks, unless one of the audio tracks is already embedded in a video. The sneaky way round that is to render the video out to WMV (or whatever other format), load that back into Movie Maker, and add the music tracks (cropped to fit as necessary). Finally, it's rendered out, and uploaded to YouTube for the world to see. I also like to embed the YouTube videos on the site at useful locations.
You can check out my YouTube channel to see my results.