Ok as per your instruction, I downloaded the AC3 filter 1.01 (RC5) from
www.free-codecs.com.
Ticked all the 'use AC3 for' boxes. Clicked OK.
Launched my player (BSPlayer 1.0) and opened the AC3 filter alongside it - and as you said, it was in use as the file played.
However, in the system tab, the Audio/Video sync slider was still sitting at zero (in the middle). Now, I'm not sure whether what you meant for me to see, was it sitting at the correct millisecond delay or if I was to manually change it. But it remained at zero and if I changed it, it made no difference to the audio/video playing in the mpeg (still out of sync).
Have I done something wrong? Does the mpeg need demuxing first perhaps?