From what i can remember from my networking days, is that Hubs divide the 10/100 network for computers, Now i dont have a 360 but this is why i hated a hub.
Get a switch, it should fix ur problem, What i think the problem is, is that the 360 doesnt see the 10/100 network due to the bandwidth of the hub being divided all over the place.
Try it, if it doesnt work, return the switch.