if you had to design a flash movie to display on a 20-inch LCD, what dimensions should set the flash stage size to?

i'm not sure, so can you tell me what the appropriate size is for both 4:3 and wide screen?

Is it a normal screen (4:3) LCD? or a wide screen(16:9) LCD? or a LCD TV?

if you wan to run your flash projector on a 4:3 LCD in fullscreen mode,
you can use 800x600, 1024x768, 1600x1200 etc...
where the height is 75% of the width.

if you have a wide screen LCD, normally is 16:9, where you'll have to set the
stage size to which hight is equal to 9/16 of width,
e.g. if you want to set the largest posible stage size (2880pixel),
you can use 2880x1620