Im downloading windows vista, when my download reached 99% it stopped, my download became 0%, what happened?
I would suggest you do some reading about how bit torrent works.
With the information you posted, which really amounts to nothing at all, all I can do is tell you we can’t help you until you learn a bit and give us some useful info about your download.
Here is a good place to start
http://en.wikipedia.org/wiki/Bittorrent
when you decide to post some more info, keep in mind that all you told us is that you are downloading one of several hundered torrents for vista
which is completely useless
and you are using some unknown version of bit comet, and connected to some unknown number of peers, from an unknown tracker.