If you have multiple computers on the router you need static IP or it will port forward what ever computer/device that get's that IP. You ahve two choices, assign a IP to the device that is not in the DHCP table of the router, or set the DHCP server of the router to assign a IP via DHCP to a MAC address of the 360/PS3/PC. Once you know the IP of the device to forward, put that IP in the router forward table. IPCONFIG, or the network setup of the device (360,PS3) will tell you your IP. But you are best off by setting a static IP that is not in DHCP.
IPchicken got your public IP (AKA ISP) from the router, what you need to put into the router is the private IP (192.168.x.x) from the PC.