Audio-video synchronisation ?

Hi everyone,
I have used BS Player for quite a long time, but one thing I don't understand is about the audio-vid synchro. When I read a divx everything is fine for a couple of minutes, then at some intervals it seems there 's a slight desynchronisation of the video and the audio. To "make up" for the gap the video part accelerates suddenly, and some of the audio is cut out. All this takes 1 or 2 seconds, after that it's ok, then here we go again...

I run under XP, with a XP 1600+ and 256 DDR RAM, so theoretically it should be enough to read divx without problems. It is the same when I record some programs and convert them to xvids. Should I buy another 256 Mb ? Thanks for any answer