Getting started with Cocoa

In order to make the software for using HID Devices with MIDI usable, it's going to need a half sensible user interface.

This video on YouTube gives a 5 minute "Hello World" overview, and was pretty straightforward to follow.

For a more in-depth introduction, the Cocoa Fundamentals and Introduction to Cocoa Application Tutorial pages over at Apple's Developer Connection are a great place to get started when learning to use Cocoa.