Over on the MSN career site, there's an article about explaining to a hiring company the short term positions (contract or full-time) on your resume. While I would enforce the importance of truthfulness (or truthiness, if you will) in your explanation I believe that thinking through exactly how you will respond when asked about these positions will alleviate a lot of anxiety. In any stressful interview situation I've been in, I've always tried to anticipate questions and think through how I would answer.
You certainly can't anticipate everything. But if you have some short stints on your resume, you should definitely expect an even minimally experienced interviewer to ask about them. It pays to be prepared.