My only internet connection at my house is through my cell phone, plugged into my PC via USB. This machine connects just fine, and I've enabled Internet Connection Sharing. I can get online with my other two PCs after I set the default gateway to 192.168.1.1. I also have a Macbook that connects to the network without issue, but can't find "the internet". What Mac setting do I need to set? Is there a single place where I can set the default gateway?
System Preferences > Network Then select the 'Advanced' button and go to TCP/IP.
Here is where you can set a manual address, subnet mask, and 'Router' (i.e. default gateway).
Here's a few pictures: