You need some hardware in between to sync the calls from the 2 machines.
http://reviews.cnet.com/8301-3132_7-57494092-98/top-five-wi-fi-routers-with-built-in-network-storage/ discusses routers that can function as such.
I currently have a portable external HDD with my entire movie collection and college documents on it. I usually plug it into my xbox and use it as a movie player and such, but whenever I want to add another movie to my collection or access my backup documents I have stored on it, I must unplug it and plug it into my laptop.
I was curious if there was a way I could connect my external HDD to both my xbox and laptop at the same time so that I could in fact access both without having to mess with exchanging cords.
I have thought about using a usb hub, but I don't know if I could split the connection for two inputs or not.