First, skim this stickie thread
and see if it answers some of your questions.
Then give some more details.
When you chopped the video into parts to export it and the sync got messed up, what were you exporting the pieces to? [wmv large/small/dv-avi/etc] How did you recombine those pieces? [wmm/vdub/etc] Is the sync messed up in the individual pieces, or just when you recombine them into a single video?
How did you cut the video into pieces? If you copy and pasted the clips, make sure you began and ended each section on a solid clip (one that doesn't fade into another). If you cut it some other way, describe it.
As a general rule, wmm 2.0's "high quality large" gives okay results. For the best results you use DV-AVI - but then you have to deal with possible sync issues (there are ways to deal with these issues, but you can avoid them if you sacrifice quality and stick with the wmv option).