How to plot frequency response of a filter?

Hi,

I am working on a graphic equalizer on PC and want to show graphically the final frequency response. Can somebody please tell me the below:-
1) Given the center frequency, Q and gain, how do I plot the frequency response, please show me simple formula if possible
2) Its a 1/3rd octave graphic equalizer, how do I choose the Q factor of each band?

Thanks and Regards,
Wonderfulaudio