Your router will have 2 IP addresses, an external one from your internet provider and an internal one for your internal network (which consists of your router and any PCs you network it to). Forget about the external address, you need to concentrate on the internal one (which most likely to be something like 192.168.1.1). Your PC will have a similar IP address which has been provided by the router (as it is acting as a DHCP server). Using the above example your PC will probably be 192.168.1.2. How do you find out? Start > Run > type in
cmd then OK. At the DOS prompt type in
ipconfig then enter. You need to configure the router via web page so use
http://192.168.1.1 as the URL then find the port forwarding. According to this
http://www.chebucto.ns.ca/~rakerman/port-table.html yahoo uses ports 80, 5050, 5000 and 5001 so forward all this TCP traffic on these ports to your computer's IP address (192.168.1.2)