I've figured out how to mask layers and what not but I want to mask specific parts of a picture. In my case I have a diagram of a heart and I want to mask the veins only, is this possible?
You could have kept this in your other post but your veigns will need to be "drawn". That can be in vector or bitmap. An easy way to do this is to load illustrator (assuming you have this because of school) and use the pen tool to "trace" all the veigns. Illustrator saves to the .ai format and Flash can load .ai. It will import your drawn image as a vector and then you can simply add it as a layer above the layer you want to mask, right-click on the layer in flash and tell it to be a "mask". Then it will mask the layer below it with the shapes you draw.
You can trace the veigns in photoshop or any other program as well. If you go bitmap (pixels, non-vector) then start with a white canvas and paint the veigns in black. Then use that black and white image as your mask.