fft / ifft implementation

Dear, 
I have decided to use dspic 30f4012 with 48k rom and 2k ram for
implementing fft/ifft. My aim is to sample the incoming voice from a mic to
the adc module for 5sec and then perform fft. I also wanted to inverse the
process to play back the voice, just to check the process. 
So please help me regarding the SAMPLING RATE, HOW TO USE THE LIBRARY
FUNCTION IN DSPIC FOR MY DEVICE, WHAT SHOULD BE MY ARGUMENTS TO THE FFT
MODULE. 
Iam using a 16 bit 28 pin starter demo board from microchip and mplab with
c30 c compiler for this purpose. 

And also am I using the correct devices for my project? 

Thanks in advance 
Siva