1. Connect the two PCs with a RJ45 Crossed Cable.
2. Create a LAN between the two PCs with Same workgroup Name.
3. After establishing the LAN, connect one of the Systems to internet through USB(no other way).
4. Now two LAN icons should appear in the System tray. One for the icons is for the System ,other one for the Internet Connection.
5. Now open network settings and select the "internet connection" and enable SHARING.
6. Now internet connection has been shared between two systems.
If you want to connect more than two PCs, use a switch/HUB.