One router can be enough, but it needs to be dd-wrt capable. Check on dd-wrt.com the models your retailer offered you for compatibility.(should be wireless N capable, 2 antennae) More details on oldwiki.openwrt.org/TableOfHardware.html
Then flash your router with the latest firmware from its producer. Do a hard reset.
After that, flash it with the appropriate dd-wrt firmware.
Do a hard reset (a 30-30-30).
Then follow the instructions found here:
If you really want 2 wireless networks, access your router at 192.168.1.1/Wireless_Basic.asp press add and you will create a virtual wifi interface ath0.1. So, use ath0.1 and ath0 instead of eth0 (wired lan) and ath0(aka wl0.1) then encrypt (192.168.1.1/WL_WPATable.asp) one of the interfaces.
Recommended setup: Do NOT use wifi for your communications as even WPA2 can be cracked. Assume that any data put on a wireless network can and will be intercepted and used against you. So, use some cables to connect your computer, xbox and whatever else you might have directly to the router. Then follow the instructions from the web page and set the iptables to deny access from/to wifi to/from the lan segment.
Two routers can also be enough:
*connected to wan (the internet)
*has open wifi access b/g/n
*has one output connected to router 2
*has the wan port connected to router 1
*has the wifi secured (mac address and wpa2)
*has the home computers connected to it.