Here are two dead-simply ways to capture YouTube videos for PowerPoint presentations (or other uses).

youtubeFisher downloads YouTube videos in several different qualities (depending on the video, HQ or HD ones might not be available).

FileBlender is a simple way to convert video from youtubeFisher to other formats (if necessary).

 Both are free and do not require an installation.

Zamzar is a free web service that will also download and convert video (and many other file types).