Now this can be done for free if you have two things: Playstation or XBOX and a WiFi router
using PS3 Media Server. (if you have theses consoles I can help you set it up)
Now buying hardware to do this you could go for something like this:
WD TV Live I haven't had any experience with these type of media servers.
Of course playing the movie files from the USB drive will depend on what format they are i:e- VOB, Mpeg, MKV, etc