MPEG video playback is skipping!!

[xxbignipperxx]

I cannot figure out why some of my MPEGS are skipping. They did not skip when they were on my Dell 600mhz, and now I have a 1.8Ghz..so I know the computer is capable...Is there a way to download some codecs to fix the problems? I am using windows media player 8.00.00.4477 running on XP Pro, I also tried using a media player that came with my ATI Radeon All-in-Wonder card and it STILL skips! Please help out...