Basically you use event listeners (the AS3 way) and then use hitTest to if it's dropped on txtfield then set the text.
PHP Code:
mc1.buttonMode=true;
mc1.addEventListener(MouseEvent.MOUSE_DOWN,mdown);
mc1.addEventListener(MouseEvent.MOUSE_UP,mup);
mc2.addEventListener(MouseEvent.MOUSE_DOWN,mdown);
mc2.addEventListener(MouseEvent.MOUSE_UP,mup);
var tempx:Number;
var tempy:Number;
function mdown(e:MouseEvent):void{
tempx=e.currentTarget.x;
tempy=e.currentTarget.y;
e.currentTarget.startDrag();
}
function mup(e:MouseEvent):void{
obj=e.currentTarget;
if (obj.hitTestObject(txt2)){
txt2.text=obj.txt1.text;
}
obj.x=tempx;
obj.y=tempy;
obj.stopDrag();
}