There are tons of free scripts that will let you do just that. You only need a server with FFMPEG support to convert the files into flv and then just stream them using any player. Peace,
I can do it for $100. nothing guaranteed yet because I havn't created a user system for file upload before. how about I'll make the script first & when I do, I'll PM you to see if you're still interested. it might take me a while to add the video part, but the file hosting I can do.