I recently installed WiFi at home - actually was pretty easy. We already had a wired network: Cable modem into a router, router with cat 5 to the desktop and laptops. All I had to do was change our old router to a similar one with 802.11b capability.
I installed it, copied all the settings, set up the WiFi part with my network card via its mac address and it works like a charm.
So yes, if you already have a wired network, you should be able to replace it with a wireless router without any problems
