You do need a computer -- I've been making all of my movies with either Windows XP, Vista or Windows 7. Sorry, I don't do Macs, but I've heard it's easier.
A microphone is also a good thing. You could however, do everything with some type of captions, but students really don't like reading. You can get a stand microphone for under $20.00 at Office Depot. For today's movies (November 8), I've been using the microphone built into my web cam.
If you want to do demostrations -- I have done a couple with the blog, you should get a web cam, and they range in price. I found one on Amazon for less than $15.00
Of course, the point of the workshop presentation was doing it without a camera.