360 video codec container support list
What format (container and codec) videos are you streaming? What Buffalo Nas do you have?
Is your 360 connected to the internet? I know there is a media update that expands the supported formats for the 360 but I think you have to actually try to play a video for it to download.
This site might help you if you are interested in researching dedicated streamers
Link
I personally use a WDTV with an attached Hard drive, and while it doesn't work with streaming on the default firmware there are some custom ones that do.