Instructions straight from Xbox support.
http://support.xbox.com/en-us/pages/xbox-live/get-started/connecting/mac-computer.aspx
So I got through Step 1 and step 2 but in Step 3, part 8, When I enter the code 225.225.225.0 for the subnet mask, i get the "setting not valid" error that says,"The subnet mask you entered is not valid. This address must be in the format xxx.xxx.xxx.xxx.
What is there to do from here? I followed all of the other steps and they worked, why doesn't this one?