Nope, that thing is a USB network device. i.e. it's *two* usb devices, one plugged into each computer, that are just connected together via a long cable. The Xbox doesn't know how to use the device so it won't do anything.
You can't turn a PC into a USB memory device because it's not possible to get a normal PC USB controller (UHCI/OHCI/EHCI) to act as a USB target, even if you change the drivers..etc. It only works as a USB host. USB is just plain not symmetrical - the chip at each end has to do a different job and they are not interchangable.
You'd need a device with a USB target chip (or USB OnTheGo, which is a single chip that acts as both, though not at the same time) such as a PDA or cellphone, rather than a regular PC.