HD led flashing when playing DVD and horrible image.
 

I play some DVD on a celeron 1,3G, but the image isn't fluid. I notice the HD led on the PC box turns on in synchro with the DVD one.
I tried both xine and mplayer and i got the same problem. Of course, i tried all settings possible with the software.
Any idea?

How much RAM do you have?
Check the RAM and CPU with "top" on console.

I got 512M of ram, and top shows nothing bad. But as i mixed different brand of ram, i'll do tests when i'll find the time to do some mechanics.

Try using hdparm to set the dma on your player, I have watched DVDs fluidly with a 64MB Vidcard and a 500mhz PIII, use either Kaffiene or Totem-Xine to play the discs, I find MPlayer to be very bad

Try including -vo xv -vf scale=-1,-1:yuy2 with mplayer to use the the built-in acceleration of the video card. The vf syntax may be wrong so check mplayer's man pages. You can try include -noaudio to find out if its the sound card lagging the video. Creative Labs sound cards drift a lot or they have poor sync, so the system have to wait.

If enabling DMA does not help, increase the size of video and audio buffer in xine. Also try increasing cache in mplayer. Turn off as many services as you can. In the BIOS, disable any cache shadowing.