What motherboard were you thinking of getting?
The P8Z77-V, P8Z77-V PRO and P8Z77-V DELUXE motherboards have onboard WiFi. The wireless antenna is on the rear panel.
So to answer your question: yes, it does replace the WiFi card, and no you won't have to buy a separate wireless card
You'll just have to install the WiFi drivers and it will work like a charm