To get them off utube all you need to do is navigate to the page with the video you want to download.
Then in safari go to WINDOW>Activity
You should see a list of files and shit. The biggest one, that will probably still be loading will be the video. Click on it and it will download. Then find that file in your downloads (default) folder (or where ever you've set up your machine to receive downloads). It should be called videoplayback.flv and should playback as such.
If for any reason it isn't an flv file just change the suffix to flv. That should fix it.