what type of files are you editing ? .... if native AVCHD then you will need a better than decent spec computer ... audio sync issues are a common symptom of a struggling computer with AVCHD.
If the sync difference is constant from start to end you could try moving the audio track left or right depending on if the audio lags or is ahead of the video, ungroup the tracks first - you'll need to zoom in close on the audio to look for a short sharp sound that you can line up with an event in the video - a car door closing or something similar .... like a clapper-board !
I am having the same problem. In my case, the clips are all HDV and the video is perfectly in sync on the timeline. When I export as WMV the final product is 'perfectly' out of sync. I use the the term 'perfectly' because regardless of the number of times it's done over the measure of non-syncronization remains constant.
Maybe this is software related and not an OS or Hardware problem.