the wireless ethernet card is used so that you do not have to actually plug a cable into your onboard 10/100 ethernet....
from the computer I am using right now, I have an integrated 10/100 ethernet as part of my motherboard, however, because there was no way i could get a wire from that to my router, i am using a wireless card to access my router that is on a different floor.......if my computer was close to my router or cable modem, i would rather have a cable, but because that isnt an option i went with a wireless card, they both offer the same thing, most laptops have both choices....the 10/100 is actually a little faster, but the wireless is more mobile....