It's a bit confusing, the breakdown is as follows:


1.) T3 "E" = dedicated international, all airlines except Skyteam and a few others who are still at T2
2.) T3 "C" = Air China domestic, but some international

The entire "T3" complex is 3.5km long like cxfan said, with the south side being "C" (called T3C in the audible announcements in the terminal), which is where you get dropped off by cars and check-in. At that same spot you can walk to the C gates.

C gates are:
1.) All Air China domestic
2.) Some Air China international
3.) Possibly some other international

Over the last few months consistently I've seen a few Air China international flights to Australia going from the T3C gates. I believe there may have been an ANZ flight departing from there the other day as well, but that could be in error I was walking fast (maybe some codeshare thing). Regardless, there definitely are some international flights that go from the C part.

The north side is called "T3E", and is where most of the international flights depart from.

E gates are:
1.) Most all international flights
2.) Accessible only by the train (departs from C part of the terminal, very easy to find).

There is also a middle concourse "D" ("T3D", accessible only by the train as well...it is the middle stop where the trains never stop) which was only used it seemed during the Olympics time, and it wasn't for commercial aircraft. Not sure what the plans for that in the future are.