found another one if you don't want to install anything. Also, a Firefox add-on :

http://javimoya.com/blog/youtube_en.php 

www.vixy.net

No, I cant download any video

In ares browser, you can download them. (Hopefully you have ares)

^what is ares? Never heard of that

just search for something like "download youtube videos"
theres a heap of sites that offer it, but a fair few dont work. just keep trying and youll find one.

youll be able to download videos as a flv file type. then you gotta find a converter. i use SUPER. it looks complicated but is actually really simple. if you want that, just search for SUPER in google.

u dont have to download them, when u see the vid it is automatically saved on the "Internet Temporal Files" directory, u just have to copy and paste it on your vid directory

Or if u r firefox user the u must download an add-on(cache viewer) then ull be able to move them to your vid directory

I use dvdvideosoft, just paste the you tube videos url and then select the video format to convert it to like Ipod, PSP, Mobile phone etc.

Firefox + greasemonkey + userscripts.org.