A/V Data Collection Using Linux?

Simon D. Levy asks: "I am consulting in a biology lab that collects data on fruit-fly mating behavior, and we would like to migrate our data collection to a Linux box. Our primary concern is being able to digitize incoming audio signals (at 8kHz sampling rate), but we would also ideally like to be able to monitor the flies' behavior using a digital camera connected directly to the computer. Crucially, we need to be able to isolate the audio component of the signal, as well as having access to an API (C/C++ would be nice) that allowed us to start and stop the recording. Any experience that anyone has had with this sort of problem would be much appreciated. We haven't bought anything yet, and are looking to build this system (CPU, video camera, A/D cards) from the bottom up. Thanks!"