Generated Flash movie (move mouse over move to see moving object):

The main idea is:

1) add external movie as sprite (movieclip) using .AddExternalSWF
2) place this movieclip to scene using .PlaceSprite and then set movieclip name using .PLACE_Name property
3) now you can access this movieclip from actionscript code using new movieclip name

In this sample we set mcl_shapes for new movieclip and then we move mcl_shapes up to mouse:

VB source code:

' ExternalSWF_AccessExternalMovieClipFromASCode.vbs

' Movie creating and setting parameters

Movie.BeginMovie 0,0,W,H,1,12,6
Movie.Compressed = true
Movie.SetBackgroundColor 255,255,255

'//////////////////////////
' External SWF
'/////////////////////////

ExtSWF= Movie.AddExternalSWF ("Shapes.swf", 3, true) ' 3 is a Sprite mode so external movie is added as sprite and returned value is a sprite index in sprite collection

Movie.PlaceSprite ExtSWF, Movie.CurrentMaxDepth

Movie.PLACE_SetTranslate 0, 0 ' set new position
Movie.PLACE_SetScale 0.5, 0.5 ' we set scale to 0.5

' now set name for added movieclip (sprite) so can manipulate with it with actionscript
Movie.PLACE_Name = "mcl_shapes"

' compiling code for enterFrame event of mcl_shapes to move and rotate movie clip to mouse
Movie.PLACE_CompileEvent "onClipEvent(enterFrame){dify=_root._ymouse - _root.mcl_shapes._y;difx=_root._xmouse- _root.mcl_shapes._x;_root.mcl_shapes._x=_root.mcl_shapes._x+(difx/5);_root.mcl_shapes._y=_root.mcl_shapes._y+(dify/5);_rotation+=10;}"

Movie.ShowFrame 1

Movie.EndMovie

Movie.SaveToFile "ExternalSWF_AccessExternalMovieClipFromASCode.swf"