Screenr can be just the ticket, This great little web-based app will let you capture (screen and audio) a short (5 mins max) video tutorial that you can post to Twitter, embed in a blog or send to Youtube. You can even download the finished video as an mp4, and archive it for future use. The steps are easy to follow and you'll be pleased with the results.
Below, I've posted a demo I made on how to access our district online databases via a school library catalog. (BTW, the yellow "glow" around the mouse in the tutorial is courtesy of http://www.2point5fish.com/ and their mini-app "Mouse Locator", for the Mac.)