Either disable airport temporarilly or make sure ethernet is higher up in your network configuration list... Otherwise it'll always just look on your airport connection for the IP you enter.
Once you do that, put the xbox's IP address in a web browser (Safari or Firefox should be fine). You should get a smartxx flash page. Use that to flash ed @ chip to the smartxx.
Once you flash that, load up ed @ chip.. Then you should be able to FTP in and transfer a dashboard. After that, reboot to the smartxx os and flash a hacked bios. Then you'll be good to go