Your modem needs to forward ports to your router... so the IP that needs forwarding for the port number should be 192.168.1.1 Now the port is forwarded to the N-Router.
Now, have the N-Router forward that port to your computer's IP
Which is dynamic, that is, DHCP (Dynamic Host Configuration Protocol) auto-assigns it. So you need to assign one manually. Google how to do it with your OS. set your computer's IP to something like 192.168.1.25 (and the Default Gateway is the IP of your N-Router, and the subnet mask will be 255.255.255.0 ) so that DHCP doesn't auto-assign another computer to be the same as your manual configuration.
For the DNS servers, I'd put 8.8.8.8 and 8.8.4.4 (Google's DNS servers; they're a bit faster than your ISP's ones usually).
Now, have your N-Router forward the ports to 192.168.1.25
Ta-da!
Well, you also have to set your computer's software firewall to allow those ports... Google that as well.
EDIT: Basically, what you are doing is saying:
1) Hey modem, forward any incoming requests on TCP (or UDP if that's what is being used) port xxxx to IP 192.168.1.1
*port requests from FS2 are forwarded to your N-Router's IP and your N-Router gets them*
2)Hey N-Router, forward any incoming requests on TCP (or UDP) port xxxx to IP 192.168.1.25
*port requests from FS2 are forwarded to your computer's (static) IP 192.168.1.25*
3a)Hey computer, instead of asking for your IP to be assigned to you by the DHCP server on the device you are connected to (in this case, the N-Router), I want you to have these settings so that you will always be available when the N-Router sends FS2 port requests to 192.168.1.25:
-Your IP on the little N-Router network will be 192.168.1.25
-Your subnet mask (complicated, but it basically makes the IPs match the correct network setup by telling where the split the network IP and the subnetwork IP addresses) will be 255.255.255.0
-Your Default Gateway on this network is 192.168.1.1 (this is the router's IP address, basically, if you can't find what your looking for, ask this guy to find it... so when you put
www.google.com, and the IP is retrieved by DNS, and you try to find that IP on the network... well, Google.com isn't on your home network, so ask the Default Gateway to find it for you... then the N-Router can't find it on the modem network, so it asks IT'S Default Gateway, 192.168.2.1, which is your modem, to find it. This process is repeated on your ISP's network all the way up until Google.com's IP address is contacted.)
-Your DNS servers are going to be Google's DNS servers: a) primary IP 8.8.8.8 and b) secondary IP 8.8.4.4 (this means that when you put in
www.hotmail.com or similar, the address needs to be converted into the correct IP address, so ask the DNS server "what is the IP for
www.hotmail.com?" -- it will then give you the current IP address of
www.hotmail.com, which your computer then uses to load
www.hotmail.com)
normally, DHCP assigns all of these options. Ultimately, the DNS servers end up being auto-assigned to your ISP's DNS servers... not always as fast as Google's DNS servers, in addition, some sites that your ISP doesn't like may be blocked. If you want to use your ISP's DNS servers, google what they are for your ISP, and put in those values here3b)Hey Firewall, allow requests on TCP (or UDP) port xxxx to be accepted on my system; don't block them
*TCP or UDP port requests are now received by FS2, and much joy results*