MEDIA PLAYER STOPS AND STARTS!!??

When running media player,video and audio files stop and
start, sometimes freezing for a few seconds. I have a
2.8ghz p4, 1gb ram, and xp home, I have no idea where to
start with this, my old p.c 400mhz, 128mb was fine doing
this, can't understand why it's happening on a more
powerful computer, please please help!!! Andrew.