I've done a few applications that use a similar setup.
I generally use an NSSplitView, with a single column NSTableView in the left pane. Don't forget to disable the headers, and make it display as a "Source View" style.
If you want the disclosure triangles, then you'll want to use NSOutlineView instead of NSTableView, but at least for the first go, I'd stick to a simple NSTableView.
A pattern I also use is to make the NSTableView slightly shorter than the NSSplitView, and have buttons at the bottom (add, delete, etc). I've usually built the program around Core Data, so it's easy to hook up these to methods to create/delete objects, and then bind the NSTableView to the array of objects.
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