Yes martyn, you're right, on a local network with the right permissions and filesharing setup, you might be able to get this to work...
BUT, you need more than just an IP address, you'd need to have the drives on those other computers shared ( possibly to the 'nobody' or 'apache' users ) you'd need the network names, permissions, etc.
And you wouldnt' really be changing things over the traditional PHP sense of HTTP, you'd be moving things locally ( only locally would be locally shared drives )