Consistent Animation of a Background Movie Clip Across Different Scenes

Simple, just add the following code to the *movie clip* actions (NOT the main timeline, in other words, make sure your movie clip is selected, then in MX click on actions)... you might want to place the movieclip within aanother movieclip (and thus apply the actionscript to the movie within the movie), so that you don't have to re-do all the actionscript for every keyframe your movie exists.

onClipEvent (load) {
    trace("ThingeePosition from Inside = "+_level0:ThingeePosition);
    gotoAndPlay(_level0:ThingeePosition);
}
onClipEvent (enterFrame) {
    _level0:ThingeePosition = this._currentframe;
}

The "onClipEvent (load)" tells the movieclip to go to the last frame recorded as the variable ThingeePosition (stored on level0 so that all scenes can access it). The "onClipEvent (enterFrame)" sets the variable ThingeePosition to the current frame that is animating.