There are a variety of ways to download YouTube videos to your computer with online services or software.
KeepVid is an online service that allows people to download YouTube videos in FLV, MP4, WebM, or MP3 format.
MP4 - MP4 files can be played with a these software.
WebM - WebM files can be played with these software.
Find what YouTube video that you want, right click with your mouse on the URL and click copy. Open up KeepVid and paste the link in the Download box. Click Download and when Java tries to load, let it. The website uses Java to generate the download links. Choose what format and video quality that you want and then right click on the link. Click on Save As and choose where you want to save your file.
Zamzar is another online service to download YouTube videos. On the Zamzar home page, click on Download Videos. That will bring you to four steps. Step one is to copy and paste the YouTube link. YouTube videos must be 100 megabytes (MB) at the most. The second step is to choose what video format that you want to convert the YouTube video to. File Info is a good resource to find what software accepts each file type. The third step is to enter your email address. The fourth step is to click Convert. When the website is finished converting the video, a download link will be emailed to you. It may take a while depending on the size of the video.