Looking for a free, cross-platform streaming media solution? Then I recommend the VideoLAN project.
Whether you need a server to stream MPEG-1/2/4 files, DivX files, DVDs, or live video on the network, or a client to receive and decode MPEG streams under multiple operating systems, VideoLAN's VLC player will do the trick.
Check out this diagram for a nice illustration of your options.
I've been using VLC mostly to playback bittorrents of TSS that I'm streaming from my laptop to another computer on my home network. I'd love to hear how it helps the rest of you!