Sometimes re-arranging the cards in your computer can help too ... that's fixed it before. Back in the olden days when digital audio was rarer there were just some systems that were just impossible to get working though. Clicks are often caused by the data not getting to the card fast enough or not being pulled off the card fast enough, so any kind of optimisation can help, there's an XP setup guide I'm sure someones mentioned in the past that might be useful