There is an EZ way to do it.
1) let video load 100% in youtube (solid red bar).
2) open "temporary internet folder"
3) sort file list by file size (largest on top, your video when float to the top)
4) find your video (look for a youtube address)
5) copy & paste to wherever you want to save it (it will be in a .flv format)
6) watch with Media Player Classic (my preferred viewer)
I'e done this 100's of times. It's easy, quick, & becomes second nature once you've done it a few time.