Which IP Address is it??? 'it'z like a mouse maze!"

[MersyOne]

OKAY;

got this probelm that I tried to FIX MYSELF 1-whole entire day;
All I am trying to do is make it so that people can download some of my remixes/mixes/etc. But I can't seem to figure out how to OPEN PORT 6346???

Which IP ADDRESS DO I USE? THERE ARE SO MANY!

(My Gear):
I Have 2 Computers Networked, One PC, One Mac
The MAC (OSX 10.3 G4) is hooked-up to the INTERNET via DSL MODEM,
The WIRELESS ROUTER is hooked into the DSL MODEM (onto the Mac),
The PC (WinXP AMD64), on the other hand, is NETWORKED (wirelessly) via the ROUTER.

My ROUTER IP IS: 192.168.A.A
My 'MAC COMP' IP IS: 192.168.B.B
My PC IP IS: 192.168.C.C

But, when I looked on "www.whatismyipaddress.com";
It says my IP address is 70.59.42.DDD

So,..
with ALL these IP addresses,

Which 'IP' address do I configure to OPEN THE PORT 6346???????

(I'm not a network expert so I hope I'm not askin' a stupid question.
I'm learning this stuff all on my own.)

ANY GURU out there that can help me a bit?

[MersyOne]

Oh yeah, BTW,

I am trying to open the PORT for the PC (NOT the Mac).


(PC I use for music production so that is why)