I will assume that the TP Link card is an Ethernet card, not wireless. You can add a second Ethernet card or use a USB Ethernet adapter to connect to the ZYxel router and share the Internet with ICS (Internet connection sharing) or bridge the two network adapters.
Any reason that you cannot just connect the Zyxel WAN port to the incoming cable that you have and create your own subnet that will have access to the Internet, but not require your computer on all the time? If you would like to do that, I can give you directions.