Is the DVD that you are using dirty or scratched? This happened to me playing a movie a month or so ago and it just turned out to be that the disc was at fault.
If it's not that, it could possibly be something wrong with the hardware.
I have a compaq presario v 5000z ,turion 2.2 GHZ ml-40 1 GB ram pc2700, dvd-rw, windows xp sp2,and the only bad thing about it is in playing dvd's...not smooth not right ,the voice is kinda skipping .
some information will be helpfull