<p>Does anyone know any good tool that I can use to perform stress tests on a video streaming server? I need to test how well my server handles 5,000+ connections. </p>

start downloading 5000+ files of the same type with different connections.  Don't really need to play them, because essentially the client video player, flash, windows media player, etc. will just be doing a download.  So if you server can handle 5000+ downloads you will be fine.  My bet is your bandwidth gives out before you server.