First do you have a router or not. Since we were all talking about cross-over cables I'll asume you don't.
Static IP on Xbox: (If you have an X3 change the IP adress in the X3 bios to Static and then choose an IP (192.168.0.5 or anything really make it totally different from your computers IP.) If not just do this. In evox go to the system setup or options and then find the network part. change the IP from dynamic to static and then type in an IP adress (if you had an X3 use the same one) of your choice like 192.168.0.5, anything different to your IP on your computer.
Static IP on Computer:
http://www.portforward.com/networking/staticip-dhcp.htm
Just go there, select your OS and then follow the steps (I've only done this with a router so I don't know if this will leave you vunerable to attack)
(P.S. if it asks for the disk than you copied it to the HD wrong)