Ok, if you're using AS3 this is going to be a bit trickier. Because of how AS3 uses event listeners you can't just pass in a variable. If you have the time then now would be a good chance for you to read up on custom event managers so that you would be able to add parameters to your mouse events.

However, there is a work around that you can use. It's not the best way (the custom event manager would be the best), but it will work.

What you want to do is something like this:
Code:
button1.addEventListener(MouseEvent.CLICK, playTheMovie);
button1.addEventListener(MouseEvent.CLICK, playTheMovie);
button1.addEventListener(MouseEvent.CLICK, playTheMovie);

function playTheMovie(me:MouseEvent):void
{
   switch(me.target.name)
   {
      case "button1":
         yourFlv_instanceName.contentPath = "sit";
         break;
      case "button2":
         yourFlv_instanceName.contentPath = "stand";
         break;
      case "button3":
         yourFlv_instanceName.contentPath = "hop";
         break;
      case default:
         yourFlv_instanceName.contentPath = "sit";
         break;
   }
   yourFlv_instanceName.play();
}
So basically whichever button you click the function "playTheMovie" gets called. It then checks the name of the button (button1, button2, or button3) and assigns the content path accordingly using the switch statement. When that is done it tells the FLV component to play the video.