I watched Lonelygirl15's videos and its all clear and stuff (on youtube). I create the same clear videos on my computer at less than 100 mb but when I upload it its quality is reduced
Her movies are professionally done that is why they look as good as they do, she has the proper lighting it is lit well and she also has a quality camera and camera man. You are not under the illusion that she is a bedroom artist doing it on a 200 quid video camera are you?
If you cough up for the right equipment and engineers you too could have very good looking videos. The content will be crap but it will look good.
Lonelygirl15 is a manufactured person in the mould of a soap opera.
I think the problem you are having is how you render the videos. You have to configure it right. Don't make it too small that you lose quality. But don't make it too big where it had good quality. But the file is over 100mb.
Using Windows Movie Maker I edited a video file in .dat format and it was saved in .wmv format. Final size uploaded to YouTube was 35mb. There was hardly any visible change in quality when played back in YouTube.