Hi,
I think VLC supports http streaming instead of progressive download. If the file is too large, progressive download is a good choice indeed. QucikTime is not open source, so I do not use it.
I have a different question related to progressive download. I have a website that is used primarily in schools. A while ago, I had tried downloading some youtube videos (and converting them to wmv and mp3 or mp4 files I think) and had put them on my site. This way, they wouldn't be blocked in schools because they wouldn't be coming from youtube. The problem was the videos played but took forever to load because the file sizes were too big. I want to try converting youtube videos again. I recently heard about progressive download. Is flash the best way to go with this, or would quicktime or something else work best? Someone also told me something recently about Squared 5 - MPEG Streamclip video converter for Mac and Windows, but I don't know much about this.