See my answer for purchasing question,
IPP for windows will work on 32 bit and 64 bit. IPP for Mac OS X is part of intel compiler professional edition, refer to this article - http://software.intel.com/en-us/articles/performance-tools-for-software-developers-how-can-i-downloa...
Its not possible to get only FFT function package, you have to purchase complete IPP package either of windows/Linux or Man OS X(with Compiler Professional edition)
Sorry, I may not able to help you much on Intel compiler issues. There is a Intel C++ compiler forum(Windows, Linux and Mac OSX ), exclusively to discuss about C++ compiler related issues, could you submit it there?