I imported a video from Mini DV tape to iMovie HD on Mac osX (snow leapord) only to find out that some of the faces in the picture were overexposed throughout the 60 minute program. Is it possible to fix or adjust the dv file's exposure with this software so it can be usable? Thanks in advance for any advice.

Depends on whether there is any information left in the overexposed areas.
If they are completely burned out, nothing can be done.
If they are just too bright, and still contain detail, use the "levels"
plugin to correct the exposure.