How do I hook up a USB external hard drive to my wireless network?
It’s not a matter of “converting” between Ethernet and USB — the component between the drive and the network has to essentially be a file server. You can buy a standalone NAS (network-attached storage) device like this or this, or if you have a spare PC lying around, you can install any number of Linux or BSD distributions that can act as a server with minimal system requirements. If you don’t want to spend the money on a standalone device and aren’t comfortable setting up a server, you can also just plug the drive into a desktop computer and share it over the network. The details of how to do this will depend on your operating system.