How do I drag and drop movie clips in a set sequence?

I need to set up a Flash swf that enables me to drag and drop a series of shapes from point A to their individual point Bs. However, I need to ensure that this can only be done in a particular sequence. i.e. shape 1 must be moved first, then shape 2, etc. If the wrong shape is moved out of sequence, it snaps back to the starting position until the user moves the correct one.

I’m a relative newcomer to actionscript, but have read the kirupa tutorial on how to achieve a basic drag and drop of a shape. However, I don’t know how to do the advanced programming in having these shapes drop in a set sequence, and haven’t been able to find a tutorial online to help…
Is there anyone here would could assist me? I’d be very grateful!

I have the following actionscript on a button within the movie clip which drags :

on(press) {
startDrag(this);
}

on(release) {
stopDrag();

if (this._droptarget == “/my_mc”) {
this._x = _root.my_target._x;
this._y = _root.my_target._y
}

else{

this._x = 350;
this._y = 300;
}
}

I need some way for the dragging and placing of each shape to only occur if the shape before it in the sequence has already been placed correctly.

I have a deadline to get this done which is rapidly running out, so am starting to panic!