There is a bookmarklet I’ve found called KeepVid which I’ve found helpful for those times when I need to capture video for presentations. Here’s how it works.
Point your browser over to www.keepvid.com
Highlight the web address www.keepvid.com and drag it into your browsers bookmark bar.
Navigate over to YouTube and find the video you’d like to download to your computer.
Highlight the web address for the video and drag it down to where it says “Keep It” in your bookmark bar
Keepvid should launch and lower down on the page, if it can be downloaded should be a few different choices of the video. Usually it’s the different file types YouTube offers.
Right click on the one you want and with any luck it will start downloading to your computer.
The only gotcha I’ve found is that some content can’t be downloaded but it’s worth trying!