Getting my second computer to access the internet

Hi, I have 2 computers (both Win7) that are networked through cable, no router, they work fine but i can only get the internet with the computer that it is plugged into. It is a 3g modem plugged into the USB. I went into the shop and he was saying something bout them carrying their own blah and not working in Windows and after a while i went crossed eyed and it all turned into blah...