Flash CS3 Help (Shape With Bitmap in Runtime)

HI,
I am A Beginner in Adobe Flash CS3
Now, i make a fla (Flash Document) file.
say, there is a bitmap (image) in the asset/Library (imported).
I create a shape with that image. (fill type as bitmap).
Now. what i want, i want to change that shape bitmap in run time using external image file (jpeg) file. I can load and change images of movie clip. But i don't want that. I want to change the bitmap of a shape (graphic symbol) by loading an external file (image file ex.jpeg)  and also want to keep aspect ratio. (say my shape size is 800X600 px and i want to load 1486x1020px image in that shape. So, it will keep aspect ratio and resize to 800x600.
could anybody help me out..

****Pleaese At least give me a suggestton or Feedback****

please check this File, May be it will help you guys about my requirement.

Don't Panic File Size is Only (410 KB) And No Password Or Any Kind of Virus) As the file extension is (.fla And .jpg)

(http://rapidshare.com/files/316519572/Flash_CS3_1.rar)

First watch test.jpg file
i heighlight some point :
1. The Graphic Symbol (Shape 2)
2. Shape 2 Fill Type (Bitmap)
3. The Image In Assest Library
4. The Shape 2 (with fill type as bitmap)

Now, The point is what i want. If you already watch the movie (Test.fla). Then, say i have a picture (D:\Pics\Load.jpg). i want to load that jpeg file on runtime in shape 2 (as bitmap fill type) and also keep aspect ratio.  I don't want to add the image to my library (asset).

Ok, could anyone help me out ....

Thanks in Advance...