Right I rendered as a .MP4 file in Vegas and it uploaded in less than an hour

However does anyone know how I can remove the black box around the video and have it to fill the screen? http://www.youtube.com/watch?v=ivWbIMRMxS0&feature=channel_video_title, as you can see part of the screen is black
Your recording is in full-screen, whereas Youtube's player is wide-screen. You'd have to re-record your video in wide-screen.
Part of the letterboxing was possibly done by your video editor, look at any settings regarding letterboxing or aspect resolution.
You can also mess around with these tags: http://www.google.com/support/youtube/bin/answer.py?hl=en&answer=146402