Correct. All your existing computers can stay wired the way they are, you're just swapping out a 4-port router for a WiFi 4 port router.
I would recommend using a USB WiFi NIC for a desktop, and a PCMCIA WiFi NIC for a lappy. The USB works better than an internal slot based NIC. You can get the unit high up on a desk or shelf for better reception.
---
“Be careful when a democracy is sick; fascism comes to its bedside, but it is not to inquire about its health.”
― Albert Camus