If you have some programming background, and learn well from examples, then you can look at peoples code on like pscode.com. For more D2 related programming, if you scour google long enough you'll find code for old d2h modules, and how they interface with d2hackit.
I would also recommend looking on google or a favorite p2p client for tutorials on basic c++, although you don't really need to know Object-oriented design to program modules...but its good to know.