Two different movies!
There are two different Flatland films for 2007. One is called Flatland: The Film, and is already available as a limited edition release (at http://www.flatlandthefilm.com). The other is called Flatland: The Movie, and will be released this spring (see http://www.flatlandthemovie.com). All rather confusing. It looks like "The Film" is a low-budget, but fairly loyal adaptation of the book, while "The Movie" is a somewhat larger-budget film with known actors, but plays fast and loose with geometric realities.
The book must be in the public domain, else I can't see how two films could be coming out within months of each other.