Easiest way is get rid of Vista.
Don't kill me. I just had to say it.
Seriously, what I tell people is to make sure you have the newest Flash Player, some people have had issues with Vista's security settings interfering with the stream. If you are able to see the stream in the regular 320x240 player but not see it at all in full screen that is a completely new one on me.
Could be something in a video driver or display setting.
I have very little knowledge of Vista so hopefully someone who knows more can help you. Make sure your Flash Player is updated for the browser you are using. If you are using IE7 you may try Firefox.
Good luck.