_IF_ your card can find the high speed internet, probably nothing with your current configuration. Thats IF your cable modem supports 802.11a/b/g wireless.
If you add another computer you might need the router if your isp won't give you 2(or more) ip addresses, or they want to charge extra.
Originally posted by Crysalis
If you dont have a router hooked up to your modem, then you are probably stealing someone elses bandwidth in your neighborhood that also has a wireless network
Good point thats probably what hes doing