Raincoat gives the Xbox the IP address 192.168.0.64 on subnet mask 255.255.255.0 Set your computer to 192.168.0.* where * is not 64 or any other number assigned to any other computer on your network. XP will set the subnet automatically, 98 needs it putting in.
No need to mess with your router, you don't require it, you are only using it as a switch/hub.
Then open a command prompt and follow the raincoat instructions. <