Re: wireless network addon to normal
Yes you can. Depends though on how your original router issues ip addresses (static or dhcp) and which router you want to continue handling that.
Router A = original one and Router B = wireless router.
Suppose A (IP address: 192.168.0.1) is handling IP addresses via DHCP using 192.168.0.2 & up, then you would manually configure B's wan ip address with a static address of 192.168.0.2 with default gateway as 192.168.0.1. Turn off DHCP on B. Wireless pc's then should receive an ip address automatically from A via B once they connect to B with appropriate SSID & encryption password (WEP, WPA).
However, you may actually find it easier to just remove Router A and install Router B. Again, this depends on your needs from Router A.