1st you need a cross over cable and know you ip address for you xbox and username/password. Mine is 192.168.1.103 255.255.255.0. change your computer ip address to 192.168.1.104 255.255.255.0 with default gateway 192.168.1.1
reboot you xbox and make sure it picks up a ip address. Sometimes it takes two or three reboots before it gets a ip address. Next
ftp://usernameassword@192.168.1.103 and you should be able to connect to your xbox. If it does not work, ping your xbox to see if you can see it. Also if your running win2k, type at cmd promt, ipconfig to see what your ip address is.
/good luck