http://javimoya.com/blog/youtube_en.php
thats a firefox extension for downloading flv files off you tube. i'm guessing it works for google video as well.
the easiest way to display .. well that depends.
I recently made my first little you tube-ish video. Im using flowplayer to display it on my blog.
flowplayer home page:
http://flowplayer.sourceforge.net/
my blog example here:
http://www.village-idiot.org/archives/2007/04/01/who-let-the-dogs-out/
I am not using a plugin .. flowplayer was very simple for me to figure out. However, I think this site has a plugin for it made:
http://mac-dev.net/blog/?p=3
I guess there's also coolplayer:
http://www.coolcode.cn/andot/wp-plugins/wordpress-plugin-coolplayer/100
I dont use that, never have, and there were posts here last week re: something about it being broke.
If you are comfortable NOT using a plugin, and end up using the stand alone flowplayer, its really not that hard, but if you need more help, holler back.