CoreGenerator is part of the Xilinx ISE software. You can download it from the Xilinx website. The webpack version is free and includes also CoreGenerator.
you should download webpack, its free, core generator is also included....webpack has some limitations.... you need to check if its enough for your needs
Xilinx has a 30-day evaluation license you can use in the time being. In ISE go to help -> obtain a license. All you have to do is sign up on their website and it will allow you to create a node-locked license!