Data isn't being delivered to the DVD software or there could be a problem with the DVD software. I would reload the DVD player software. Download ENDITALL and use it to turn off all other applications running in the background prior to launching PowerDVD. Also try the movies that skip with another home player.
Finally, you may have a marginal NEC drive. How old is this drive? A dirty laser lens could cause a similar problem. Notebook tend to gather a lot of dust particles. A drop could also mis-align the laser mechanism.