Hi Master Ali,I'll briefly try to answer your questions for you. For more information I would take a look at the product pages of each title. They will explain much more than I can tell you here.
1) If you are looking to work with real people rather than avatars then you will want popVideo Converter 2.0. This allows one click alpha channel creation using green or blue screen backgrounds. For creating widgets like those on the home page you will want to look at WidgetCast which is used for this type of output when used in conjunction with iClone4.
2) The YouTube tutorial you refer to was posted before the release of popVideo Converter 2.0. Now you can achieve the same thing in popVideo 2 with just one click.
3) Creating a popVideo is only really possible if you have either a green or blue background and the person in the video isn't wearing any green or blue (depending on which one you use). This is an industry standard practice and is used in movie and television production all the time. Sadly you can't just take any piece of video with a normal background and make a popVideo or transparent background from it.
4) To find out all about the individual features of popVideo Converter 2.0 and WidgetCast please visit the product pages. You should find everything you need to know there.
Thanks.