The Season Three Arena Title Calculator by Arena Junkies is created by some pretty involved techniques. They start by plunging a few teams in each bracket and battlegroup as far down the ranking ladder as they can possibly get. Then, the theorycrafters at Arena Junkies do their very best guess about how many teams are inactive. Using that data, they math out what ranking you'll probably need to achieve a given title. As AJ points out, though, this is just an estimate. They don't have the behind-the-scenes data anlysis to guarantee what will be required, and the ranks will be at least a little fluid until the very end. However, as you grind your Arena ranking as high as you can tonight, this'll give you an idea of what title you might expect when S4 starts. Assuming you meet the requirements, of course.
The Curse announcement last week was a little more vague, and there weren't definites about what the partnership would mean for Arena Junkies. According to Tyveris, the existing staff members are still in charge of the site, and very little will actually change. What it will allow them to do, however, is add new features in the coming months. It'll be interesting to see what those features are, and whether it's part of that premium package that was mentioned a few months ago.