if you don't want to watch hd content, the old xbox1 can be modded with xbox media center - it can stream right from your pc to your tv.
if you want hd content, the xbox 360 can do this with a program called TVersity. However, you need a fast pc to play hd content not in the 360's native format (wmv-hd) because TVersity needs to transcode on the fly. Its pretty easy to find stuff formatted for the 360 tho, as the release groups for such videos are now doing them primarily in wmv-hd before they do .x264 stuff.
it took me about a day to get everything setup properly, but I can now stream all video, including 720p, 1080i, and 1080p as well as audio (it can't do 24bit flac yet) and photos.