would it be possible to make an app that makes it able share the wireless connection of the Wii over the usb lan adapter to be able to use it on my Xbox 360 so I don't have to have a separate Cat-5 cable running to my entertainment center.
That would require a new IOS module one that would always be loaded, it is technically possible, but I don't think you will find anybody who wants to do it that also knows how to do it.