Now that we've got X3 flashed, you'll be greeted by X3's main configuration screen.
Figure 3: X3 BIOS Config Screen
By default, the Xbox will use the static IP address 192.168.0.1 which can cause problems since most consumer routers default to this as well. Navigate to the Network Settings menu (Settings > Network Setup) and enable DHCP or assign the Xbox a valid static IP address. Also take note of the FTP login and password, by default x3 and x3. It's safe to leave the defaults here, since XBMC also runs a FTP server that supersedes the BIOS.
Figure 4: Enabling DHCP
Next, disable the hard drive lock to allow us to copy XBMC to the Xbox's hard drive.
Figure 5: Removing the Hard Drive Lock
Return to the main screen and "Cold Reboot" to have the new settings take effect.
Now that the Xbox is up in our network, connect your favorite FTP utility to the Xbox's IP address (listed in the lower left on the main screen, 10.20.7.59 in my case), create the directory "apps" on the E: drive and copy over the XBMC folder into E:\apps. (Note: X3's FTP server is pretty basic so fancy FTP clients may not work too well or at all. gFTP in linux works great as does FlashFXP in Windows.)