If you’re heading to Beijing for the Olympics, check out the Beijing Visitors’ Blog for some common Chinese phrases. You can listen and practice some basic words. There’s another recording of numbers in Chinese.

If you’re visiting China for a longer time, I have to recommend ChinesePod. They offer 10 minute Mandarin lessons by podcast (which is way better than the half-hour blocks you need for language tapes), and lessons are searchable by subject, so you can practice phrases and vocab for different situations.