Couple of terminology I guess I should get out of the way for consistency's sake throughout the post: External Router/Modem - SMC 8014WG - External IP 220.127.116.11 - Internal IP 192.168.0.1
Internal Router - LinkSys WRT120N - "External" IP of 192.168.0.175 - Internal IP 192.168.1.1 - Connected via Ethernet Cable (a really long one, from the basement to the second floor)
PC - IP 192.168.200 - Connected Wirelessly via WAP2 Personal.
Laptop - Used to try and diagnose the problem, a 4th machine to the setup which won't be part of the final setup once everything works.
The actual problem:
I've tried setting the LinkySys router as a DMZ'd client on the SMC router, and then DMZ'd the actual PC on the LinkSys. So the DMZ looks like this: On the SMZ, client with IP 192.168.0.175 is DMZ'd. On the LinkSys, client with IP 192.168.1.200 is DMZ'd.
I then tried port forwarding the necessary port on the SMC to the LinkSys (lets just say, port 80). Then port forwarded Port 80 on the LinkSys to the PC. Same as the DMZ scenario above, but change DMZ with port forwarding.
No dice, still :(.
Now here's where I went stupid--and tell me if one should never do this--I enabled both DMZ and port forwarding at the same time. I fired up Opera--my browser of choice ;)--typed in 18.104.22.168:6333 and...
... Third time is the charm they say? Well, clearly not. Otherwise I wouldn't be here ;).
To diagnose the problem, I enabled "Allow remote access to the Admin panel" on the LinkSys router, and specified port 6333 as the port to use. I port forwarded port 6333 on the SMC to 192.168.0.175, and access my external IP of 22.214.171.124:6333 in hopes of seeing the Admin panel... No dice (I think I've ran out of dice by now ;)). So to see where the problem was, I connected a laptop to the SMC via LAN cable, and typed in 192.168.0.175:6333, and viola, Admin Panel access!
So the problem looks like it lies with the SMC--But that's as far as I've got, I've done the port forwarding, the DMZ'ing, and I've even disabled the built-in firewall for safe measures, but nothing worked.
So, here I am. Unable to connect to the PC behind the Internal router externally, and without anything to go on other than to come here and ask for the wisdom of the the superuser folks :).
If any more detail is required, just ask.
(Apologies in advance, if questions should never be this long winded!)