I've got port forwarding working now. The ports are not able to be pinged if I don't have the application running that requests to use the specific port(s).
One thing I think that might have been happening is that the firewall was blocking outgoing traffic as well as incoming. I went back through and carefully reworked all of the port forwarding, and I added an IP filter that allows all traffic outbound from my PC's LAN IP. I had a relative of mine test a port on my end for a running server, and it worked.
I also had a dedicated game server running for an hour or two earlier this afternoon (many people joined).
So here is how my router/computer are set up at this point, for anyone who may need help in the future. Make sure to have your router's switch set to ON.
1. Go to Internet LAN -> DHCP lease and set your PC to manual.
2. Go to Security -> Firewall and deselect "Block Ping from Internet."
3. Add an IP filter (Security -> IP Filter) to allow outbound connections from your PC's IP to any destination (leave destination blank), and allow for all protocols. Make sure the operation is set to Enabled. If you wish, I suppose you could make the allowed protocols and ports more specific, but there's not really any need to.
4. Set up your ports in port forwarding (LAN Config -> Port Forwarding). I would recommend portforward.com for finding ports that you need enabled for a particular application. Use the Buffalo WZR-G300N for the Manufacturer/Model. I do not recommend using the port forwarding wizard on the router's Setup page. If you want TCP and UDP for the same port range, you have to specify it twice.
5. Set UPnP to enabled (LAN Config -> UPnP). That setting was enabled by default on most other routers I've used (other brands), and it's used by a lot of different programs. If you have it disabled, you might run into some problems.
6. Set your computer's IPv4 settings manually. Type cmd into run from the start menu (you have to type run first on Windows 7 if you don't have it added to the start menu), and then from that point, type in ipconfig /all. There you will find the information you need for the IP address (your PC's local address), and the default gateway. The subnet mask is usually the default. Visit the Diagnostic -> System Info page to get the IPs for the primary (preferred) and secondary (alternate) dns servers.
7. Be sure that your OS's firewall and antivirus settings are set so they allow the program(s) to access the internet.
Other notes: Apparently this router does not support NAT loopback, so you'll only be able to see or join your own local server as/from a local address (192.168... for example), while others from outside your local network will be able to see it from your ISP assigned IP address (so long as you have your program set up correctly). You also won't be able to ping a forwarded port unless there is a running application that is currently/actively using that port. I would recommend using canyouseeme.org or yougetsignal.com to test a port to see if it responds (while your application is running, such as a dedicated game server).
Good luck.