XP playing movies problem

[cobrax2]

I have this problem for a long time now:
When i try to play a movie (mpg, avi) it will not play smoothly.
I mean that it play perfectly for 5-10 mins, then it stops for about half a second then it catches up and plays again perfectly until the next time
This happens for every movie!
In Me/98 i dont have this problem at all!
I supposed it was the hardware, but i just changed it

I had an AMD Athlon@1200/384SDRAM, 20G/7200RPM, Nvidia Tnt2pro 32, Yamaha 724 pci, tuner tv Leadtek, MB Azza.

Now its an AMD XP 1900+/512DDRam Corsair/ 20G+40G/7200, Gigabyte Radeon 7500, Yamaha 724, tuner Leadtek, Soltek DRV5 MB

So it is actually an new computer! the problem is the same.
Afer SP1 it also sometimes stops responding (mediaplayer, not the computer), so i press ctrl-alt-del and kill it, and restart it and plays fine again until next time