In your situation I don't think the magnet will cause a problem to the computer, just keep it away from the monitor (if it's a CRT), and any floppy disks. The problem might come from excessive vibrations if you turn the bass up loud.
I can see that both the pc and xbox have the same address which is a no-no. (192.168.1.103) Change the xbox to be 192.168.1.104 I still don't see how you could connect the internet and the xbox to your pc at the same time. How are you doing that?