I disagree that you have to start a new project. It's actually pretty easy to integrate CoreData into an existing project - a good starting point is to create a new CoreData project, but copy the code it generates into your existing project (examine carefully the app delegate to see what it sets up). There's really not that much code involved, and it's easy to create new data models.
It's also a really good idea to work through Apple's CoreData tutorials to understand what is going on, and there are some good books as well.
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