There isn't an out-of-the-box blog solution, at least not that I am aware of (maybe it's part of some interface package, not sure). In eZ Publish you can customize everything about the blog, but you will have to put it together yourself, so if you're not an eZ developer, you will have to ask yourself a question: do you want to become one? If so, you will have to study eZ Publish quite a bit to be able to accomplish that. If not, then just choose one of the dedicated open source blog platforms that are out there and start using it - you will be much better off.