Trouble with ethernet splitter

I recently bought an iMac OS X running 10.8.1
I'm a university student and my room only has one ethernet port in the wall.
Last year i had a really old powermac and used this ethernet splitter to use with my xbox aswell

5 Port 10/100 Ethernet Network Switch LAN Hub RJ45: Amazon.co.uk: Electronics

But once i plug the mac into the ethernet splitter it takes all control of the internet.
The xbox wont connect nor will the mac if something is plugged into the first port.

Is there something in the mac settings i can change?

If the port you have in your room is an ethernet port and not a Wan connection there's not much you can do. Have you tried attaching a router to that connector to see if it will work? If a router works your problem is solved.

Agreed with chscag. A Switch does not provide DHCP IP Address's. A Router will. give that a try if you can. Agreed on the WAN Port. I would bet it's not handing out more than one IP address.

Don't be surprised if solving this problem does not involve a chat with some support folks at the university. Many organizations with large numbers of users frown on individual users setting up their own routers. When not done properly it can cause interesting problems.

They most likely have port security turned on, allowing only a single MAC address per port. Thats how I set my switches up, but defo a good idea from Slydude to check with your uni folks.