ATeve,
As far as I can tell, there is no documented details on how to enable Back To My Mac with non Apple routers. NAT-PMP stands for (basically) Port Forwarding, which most routers do have. LET ME CLEARLY STATE: I have no idea if this is actually what's supposed to happen. I only know how port-mapping works in general, and so have extrapolated the configuration posited here.
The basic idea of port forwarding is when a service tries to connect to your network over specific ports, you can forward those requests to any IP in your local area network. I have no idea why this information is so obscure, but the ports that need to opened SEEM to be 4488, 4500, 5354, 500 (look at http://support.apple.com/kb/TS1629). BTMM uses two different protocols, TCP and UDP (the referenced url clarifies which port is which protocol).
When you go to your router admin to set up port forwarding, the entry form is something like this (the IP is IP of the computer you want to forward to):
Protocol IN OUT IP
UDP 500 500 192.168.0.10
Basically, this kind of set up takes the incoming request and forwards it to the right computer. As I said, there are 4 ports that BTMM seems to use, so there'd be 4 rules added to your router.
SO... I THINK that's how this is supposed to work. What I don't understand is why there's no documentation about this. "Enable NAT-PMP" really makes no sense, as it's not really a general on-off switch. The other thing that I don't understand (and, to be honest, what makes me question whether I'm correct in my understanding) is how this could work with multiple computers behind the router, as I have. You can only direct one incoming/outgoing port; I have no idea how you configure the right request to go to the right computer.
I couldn't see a router that specifically matched yours, but there are screen shots at http://portforward.com/english/routers/port_forwarding/Gateway/Wireless-Cable-Ga teway/Apple_Remote_Desktop.htm that may be similiar. The ports shown here will be different, but it will help you.
If you do try this kind of IP forwarding setup, I'd be interested to know if works for you.
AGAIN, total disclaimer, I have no idea if this works, but you should be able to delete the port rules if it turns out not to work.
Hope that helps.
