Note: The easiest way to capture videos to your desktop is to copy the URL (web address) of the video, and then go to http://www.savevid.com, and paste it into the field with "Paste the address of the video you want to download" in it. You then get a number of formats in which that video is available. mp4 is probably your best bet. You may have to convert it for PowerPoint, if you have an older version of Windows and/or PowerPoint, using Pazera mentioned below. Macs play well with mp4s. If Savevid doesn't work, keep reading:

 

Directions for downloading certain types of videos (like those on YouTube) and converting them for use in PowerPoint (Windows) or Keynote/PowerPoint (Macintosh)

Video Downloadhelper for...

Windows:

Download and Install:

FireFox from http://www.mozilla.com

Launch FireFox, thein go to Tools>Add-ons and Search for and install Video Downloadhelper.

Go to YouTube and choose a test video. (note: Firefox may ask you to re-install Flash Media Player. You will be walked through the process)

There will be a gray triple balloon looking icon on your toolbar that will turn to colors and rotate when there is a downloadable file. Click on the triangle next to the rotating balloons and choose the video format you want to download.

changes to Active Video Downloadhelper Balloons

NEW - Some videos have an 720p or ".mp4 "next to them. If you download them, and the are .mp4 files, you should be able to insert them into a slide in PowerPoint as they are. If you need to further convert the .mp4 file to a .mpg or .wmv because it will not play in your version of PowerPoint, download the WinFF converter here or Pazera Converter here.

However, you may not have the option to download an mp4 or 720p video, and may have to download the video as .flv, or Flash Video, files. This is especially true in some other sites with videos. If this is the case, you can use Pazera's free converter to convert them to usable mpg files:

You can get Pazera from http://www.pazera-software.com/products/flv-to-avi-converter/ (or http://www.download.com/Pazera-Free-FLV-to-AVI-Converter/3000-2194_4-10786669.html). Even though it says FLV-to-AVI, it also converts to MPG. Try WinFF converter too(see above), I've not had a chance to try it, and thus cannot recommend it, but I've read where it would convert .flv files.
Also, if you get files from Wingclips, they are .mov files. In order to play them in PowerPoint easily, you will want to convert them to .mpg files using Pazera's .mov to .avi converter, which works the same.

To use Pazera's FLV to AVI converter,

1) Find the downloaded video (there is a Video Downloadhelper folder in your documents directory, but you can also choose to download it to your desktop). Drag it and drop it on the Pazera Free FLV to AVI Converter shortcut (or program file).

2) Make sure the MPG button is pressed.

6) Click CONVERT. Voila!

Macintosh (Tiger or Leopard)

(Note: .m4v files play well in Keynote, but not in PowerPoint. You can convert an m4v to mp4 by simply changing the extension, they are the same file types.)

Download and Install:

FireFox from http://www.mozilla.com

Launch FireFox, thein go to Tools>Add-ons and Search for and install Video Downloadhelper (There is a full tutorial on using Video Downloadhelper on YouTube that may save you from reading the rest of this page! It shows a Windows version, but it works the same).

Go to YouTube and choose a test video. (note: Firefox may ask you to re-install Flash Media Player. You will be walked through the process)

There will be a gray triple balloon looking icon on your toolbar that will turn to colors and rotate when there is a downloadable file. Click on the triangle next to the rotating balloons and choose the video format you want to download.

Inactive Video Downloadhelper iconchanges to Active Video Downloadhelper Balloons

NEW - Some videos have an 720p or ".mp4 "next to them. If you download them, and the are .mp4 files, you should be able to insert them into a slide in Keynote or PowerPoint as they are. You are then finished.

However, you may not have the option to download an mp4 or 720p video, and may have to download the video as .flv, or Flash Video, files. This is especially true in some other sites with videos. If this is the case, you can use one of the following converters to convert them to usable files:

Video Monkey: Drag and Drop the .flv file into the window, and press the start button.

or

MPG Streamclip: Drag and Drop the .flv file into the window, and go to File>Export... and choose a file export, MPEG-4 (.mp4) being on of many choices.

or

TVTube: Launch TVTube and convert it by going to File>Convert Files... and navigating to the file. Save it for iPod, and it will play well in Keynote. If you change the extension, .m4v (which iPods like) to .mp4 in the Finder, it will play well in PowerPoint for the Macintosh as well.