I used Open Transport when I had to use networking. Apple's Carbon documentation for it is HORRIBLE, but you can still get Inside Macintosh: Open Transport from the Classic section. Quite a good book but only covers up to Open Transport 1.3.
Inside Macintosh: Open Transport, the O.T. technotes and looking up stuff on XTI ( what Open Transport was based on ) managed to do the trick for me

~~

You could also just try using BSD Sockets itself. From what I understand, they have somewhat better performance than Open Transport( which on OS X is just a wrapper on top of BSD Sockets )
check here for a page on BSD Sockets : http://www.ecst.csuchico.edu/~beej/guide/net/html/