I think you can download Audacity for free. Google it, and it should turn up.
There are a couple of variations on this theme. One is just to use a microphone, and I've done this, and it works for some kinds of shutters, as long as you understand how the shutter works and can interpret the peaks in the waveform. Some shutters have too many noises going on to separate out the different events happening during the exposure. First test a slow or B exposure to see what opening and closing look like.
Another variation is to use a photocell with a simple amplifier circuit plugged into a sound card. This measures light, so it should be easier to interpret with any shutter. I've seen one or two schematics for this sort of device on the net.