If you just want to stream you tube videos, you can just visit the website through your default browser and watch the videos. Doesn't require any application. If you want to download you tube videos to watch later on, then you'll have to install apps specially designed for download. As already mentioned you tube downloader and you tube downloader pro are two such apps.
blitZkid
Nokia C7: Running on Nokia Belle
"If I'm helpful in anyway, a click of appreciation on the star would be nice"