Stochastic Resonance

Dear CCL Users,
                I am trying to calculate Signal to noise ratio for a
 stochastic system (with white noise). I can't understand how to calculate
 the noise power and signal power? Is there any free fortran/C progam
 available for this? Any kind of help is greatly acknowledged.
 Thanking you.
 With regards
 Utpal Sarkar
 Indian Institute Of Technology