First of all, lets not encourage users to break any laws or rules set forth by either their ISP and such. If you do so, we will close this thread. http://www.linuxquestions.org/rules.php
Second of all, I truly don't think your system would be able to handle streaming a video to 200,000 users all at one time, especially on a cable modem with your upload most likely capped off at 128kbs tops.
If you want to perform something like this, I'd say pay for a cheap hosting provider offsite. Usually they are equipped with the servers to handle such traffic and are usually on T3 lines, etc.
I'm sure if you tried, your ISP would notice the amount of traffic to your modem on a particular port and shut you down. Trust me, I know they can do this and they monitor for such things. We'd shut someone off for having a virus within a matter of hours in some cases.