Now we see the picture. You should tie the X Box into the router with a ethernet cable. But if you want to bo from X Bos to the PC, you may need a crossover cable. Take a look at Network connections. The wireless will be OK and the Ethernet will have a red X on it or a yellow triangle. That is when you have the wrong cable. Standard Ethernet cable is for going from a client to a router.
While on that point, new routers are "smart" can can fix the cable connection. Booth NICs used in PCs are still the same.
You can run Ethernet cable over a 100 meters, about 300 plus feet, and still get 100mbps
Also, your X Box can do better with a direct connection to the router.
But it should work with a crossover cabvle. Onace you got that, you need to bridge the two c onnections.
In Windows XP, Stgart > Connect to > show all connections, bridge connection
But if you don't have two connections to bridge, you will see: