What kind of devices do you want to stream video to? Regular computers? A playstation? Other media center devices?

If you're targeting UPnP-compatible devices like e.g. a Playstation 3, I've previously setup MediaTomb on Ubuntu, and it worked like a charm. If you're targeting Windows computers, you might as well create an SMB share, and just stream videos like you would share any other file over the network. If you have clients running lots of different operative systems, a plain FTP server should work fine. A simple HTTP server (lighttpd or quickserve) could work too. Or are you looking for a different kind of solution?

I'm not really familiar with that kind of software. If you are willing to do some coding yourself, and have some extra time, you could install a real web server (apache or lighttpd), and hack together a CGI script that automatically generates web pages with embedded video streams.

Given the right multimedia plugins on the client side, it might also work to just point quickserve/lighttpd/apache directly to your media folder - the question is then if the clients will download then view the files, or display them in fullscreen inside the browser. Anyway, this alternative would not result in small embedded video like on youtube or a flash interface, if that's what you're after.

In any case, I'm sure this problem has been solved independently a tenfold of times; some googling should reveal other and perhaps more polished alternatives :-)