It is not possible to connect an iPad using a wired (RJ-45) Ethernet connection. The only connection is via Bluetooth, WiFi or 3G. The iPad has a 'pseudo' USB connector cable assembly that allows you to connect it to the USB port of a PC for synchronisation and to the Camera Connection Kit, which enables connection to USB-equipped cameras and also SD cards. It has a very limited current drive capability of 10 mA - compared to a 'regular' PC USB port's capability of 300 mA, so there is a very limited list of peripherals that can work with it.
Tim