Here's what I've done to check the position of the video, I used it to determine the end of the video as the NetStream.Play.Stop event was delayed in player 7.
So you can do this to track the position and act accordingly

time_interval = setInterval(checkTime, 500);

function checkTime() {

end=Math.floor(flv1.netStream.duration)-Math.floor(flv1.netStream.time);

if (end==0){
clearInterval(time_interval)
}//end if

}//end check time