A/D and D/A Boards for Linux?

Quadropleen+ asks: "I work in a lab where we do real time control of industrial hardware. To this point, we've been using several old A/D and D/A boards to control these processes under DOS, due to the anti-real time properties of Windows. Well, our cards are beginning to fail, and we're looking for replacements. I've been trying to get my advisor to move to Linux, and I see this as a great opportunity to leverage a better OS onto our machines. Does anyone have suggestions/experience with using A/D & D/A boards with Linux? What are the best and worst ones out there?"