How do I get an NSArray of filenames of all files in a given directory in my app?

What I want to do seems simple enough: Get an array of filenames in a given "directory" on my app. But the more I play around with NSFileManager and NSBundle I find myself getting more lost...I just want to get the filenames of the files organized in a specific directory in my iPhone Xcode project...For example: The directory in question is called "Images" (created using "Add > New Group" under the project icon in Xcode) and contains 10 .png images. It seems simple but I am getting nowhere. I'd appreciate some help in finding the answer.

Q: How do I get an NSArray of filenames of all files in a given directory in my app?