If you are trying to connect to the internet through his computer he either needs:
2 Network Cards: One connected to the modem, one connected to your computer.
Or
1 Network card: connected to your computer and the Modem connected to his computer via some other method (USB)
You need to set up 'Internet Conenction Sharing' on both computers.
You should set the Network Card on your mates machine as follows.
Card connected to your computer should be:
IP ADDRESS: 192.168.0.1
SUBNET MASK: 255.255.255.0
Card on your Laptop should be:
IP ADDRESS: 192.168.0.2
SUBNET MASK: 255.255.255.0
GATEWAY: 192.168.0.1
That should be it. If you are using any firewalls make sure addresses 192.168.0.1 - 192.168.0.255 are set to the Trusted addresses entries.