Is it possible to capture all the sound from a computer and have it pass through a equalizer before reaching the speakers?
How can you program a band pass filter on it?
EDIT: I'm trying to get this on Windows (with Python? heh) but if there is a generic, cross-platform approach that would be great.
You can implement an equalizer either using discrete bandpass filters or you can do it in the frequency domain (FFT -> equalize -> IFFT). For bandpass filters you can either combine a lowpass and a highpass filter or you can use one of various common designs, such as a damped resonator.
How you actually implement the above will depend on what OS, programming language, etc, you are using.