Cpu resources at 100% watching movies

Hi guys, need your help.

my laptop is about 18 months old, a Sony PCG-FRV25 it has the latest driver, directx avaliable with Windows XP pro SP 2.

when i watch movie files, avi,mpg, dvd, the computer would lag and the program that's showing the movie would tkae up to 100% resource, i've tried on WMP, Winamp, powerdvd.

when watching avi,mpgs, the frames would lag. the sound would be fine.. but the movie itself slows down.

when wathcing dvds on powerdvd, on the normal play mode, the movie plays like 4x the speed.. when watching on wmp, the movie plays fine for awhile then starts to keep jerking.. like showing only pockets of movie at 1 time.

Anyone know how to fix this? it's been this case for the past 2-3 months i'm all out of ideas.