how you 'insert" gif? if you load it at runtime then simply first frame is only displayed:
If you load an animated GIF file, only the first frame is displayed.
I used <mx:Image....
well you mean NO way see an animated gif?
I don't know how you created your Gif, but if it is on Flash you have to put all your image on the First layer, it's not permitted to put them in MovieClip's layer
i think used Fireworks cs4 ... well how detect in gif that you say? is any way[First layer or MovieClip's layer]?