On CakePHP's Bakery blog Joel Perras has made a new post that, he hopes, will clear up some of the confusion around which versions of PHP will be supported in which CakePHP release.

There seems to be a bit of confusion as to what version of PHP will be supported in what CakePHP releases, and where to find which projects on http://code.cakephp.org/projects. Hopefully, this post will help answer any questions you may have. If you only read one line of this entire post, read this: CakePHP 1.3 != Cake3.

Basically, PHP 5.3 support is being worked into the 1.3 series of the framework but not the 1.2 versions. Currently, though, the 1.3 branch isn't considered stable. There's also a distinction made between the CakePHP 2.0 project and the CakePHP 3.0 project.