It's doubtful your computer has an internal modem. If your new ISP is going to provide you with a dialup connection then you will need to purchase an external modem. If the ISP is going to provide you with a cable or DSL connection, then they will generally provide you with a modem (you lease or rent it from them on a monthly basis). Your computer will need a nic (network interface card) in order to be connected to the provided modem.