Ok... I figured it out, and managed to host a Netkeen game - though it was really laggy, to be honest. Better to let someone else host, but nice to know that I can do it if needed.
Of course, I had to read the instructions that came with my modem/router - these are going to be different for everyone, probably. But opening up the settings in Midori (fixed version) worked just fine.
In my case, I set it up so that UDP port 3140 is forwarded. I'm using Bell, and there was no "forward ports" option - instead, there was a list of Applications such as "Age of Empires Online" and so on. I created a new "application" called "DOSBox" with the correct settings, and selected that.
I also had to select my Pandora in my "home network" settings; I had two local devices using my Wifi connection (my Pandora and the desktop PC), so for a while I was stumped because I had opened port 3140, but it was assigned to my desktop PC, not the Pandora.