Trouble Sharing Intenet Connection

Hello,
I have a small problem and need some help. I am trying to share the internet connection with my Pc and XBOX.
Here is the set up

2 Computers
1 router
1 XBOX

I have 2 Ethernet ports on my PC, I have a crossover cable connected to the XBOX and one of the ethernet ports on the computer.

I use the other ethernet port to run to the internet.


Now on the router there is another PC connected.

My problem is when i try to use connection sharing to connect the xbox to my PC I get en error about the IP already being assigned.

I just can't hook another line to the router and then to the XBOX since I live on another part of the property than where the router is. Is there anyway to share the Internet connection without this error?