How to take the FFT in a limited range of frequencies?
If your sampling frequency is $f_s$, and you calculate the FFT with $N$ samples, then the FFT calculates the signal's spectrum at $N$ frequencies from $-f_s/2$ to $f_s/2-f_s/N$, inclusive. In Matlab notation, this would be written as:

freq_vector = (-N/2:N/2-1)./(f_s/N);


(Note that you have to shift the spectrum returned by the FFT operation to correspond to this vector; in Matlab, you would use fftshift.)

I don't know of any FFT algorithm that lets you restrict the frequency range. I would suggest using Goertzel's Algorithm to find the spectrum at the particular frequencies you're interested in. You may also use a bandpass filter to eliminate the unwanted frequencies before performing the FFT.