Scaling a Stroke Object
Flash CS3 Tutorial
How to Scale a Flash Stroke Object with or without Scaling the Line
Stroke objects can be created with the Pen tool, Pencil tool and Line tool. When you first create the object it has a stroke, but no fill. If you attempt to scale your object with the Free Transform tool, Properties panel, Subselection tool or Transform panel the line weight never changes.
However, if you want the line weight to scale as you enlarge the object it must first be converted to a symbol.
Create a stroke based object with the Pen tool.
Select the object and convert it to a Movie Symbol (F8)(Modify > Convert to Symbol).
With the symbol selected, choose the Free Transform tool (q key).
Scale the object by clicking and dragging the transform corner boxes and the line weight increases.