[CentOS] CPU usage

Does anyone have an idea why cpu usage varies constantly, from as low as
4.X % to as high as 20+%? All that I have open at the time of running
"top" is the gnome-terminal. The reason why I'm hunting this, is that I
just can't seem to play DVD's (using Xine) without choppy playback
(sound is fine). I know my laptop is aching - running CentOS 4.4 with a
Celeron 800 and 256MB RAM (DMA's turned on), but still - I think it
should be able to play DVD's, or not? I have the feeling that the more I
can tweak CPU usage, the better my chance of success will be. Any advice
would be appreciated.