DSL through Ethernet but not USB?

My mother just got a new COMPAQ Presario Laptop with Windows 7.

Previously she had a COMPAQ Presario Desktop with Windows XP Home, which we connected to out DSL modem with a USB cord.

I myself have a rather old Gateway using Win 98, and the only way I can get internet is through a Ethernet cord. With this new laptop though the only way she is able to get the internet is through an Ethernet cord, as when I plugged in the USB cord there was no internet at all.

Is there a way to get it through the USB cord as we had it before so both of us can have internet without having to switch Ethernet cords?

Probably not. Get a little ethernet switch like e.g. this one and you can attach multiple PCs. Just plug the ethernet cable from the modem into one port and then one cable per PC into the other ports. The port sequence does not matter.