Not so good...
I think its retarted manually importing a sprite sheet and then manually breaking it apart and making movieclip symbol sprites this way. Why? Because:
a) You can just import the whole sprite sheet via code at run time from the folder that your game s in, this way you can always change the sprite graphics without having to recompile to whole fla.
b) If you have the sprite sheet imported and cached in a bitmap data object you can copypixel any sprite from it into a dynamically created movieclip and animate it automatically.
c) That all only takes a few lines of code and can be done in 5 minutes compared to the hours you waste if you do it your way.
greets