I was looking for something to do this last month at work and came across:
http://camstudio.org/
It was originally built as a free product, but over the years, it got purchased and repackaged and resold many times over, to the point where the current version is built into Adobe Captivate. However, you can still download the last free version, which does a great job of capturing screen content.
It has very few settings, so it's easy to setup. One warning: By default, it records 200 frames per second, so if you're recording full screen, your file will be huge (your hard drive probably wouldn't have enough room for 4-6 hours). Fiddle with the settings to get a manageable file size, but other than that, it does one thing, and it does it well.