Flash CS5 - Seperating an image from a sheet

I'm not sure what I'm doing wrong for this simple task.
I have a sheet and right now I only want to use a small portion of the sheet.
I try to click on the sheet and it moves around.
I lock it, and I can't select any part of it.
How do I separate it?

BTW does it matter if it's a symbol or just a PNG sheet?

What do you mean by "sheet"? If you mean you have a large image and you only want to use a single part of it then you have a few options. Personally, I would cut that one part out in Photoshop and then import it on its own. Another option is to use a mask in Flash. To do that in Flash, create a new layer above the one with the image on, draw a rectangle or whatever shape you want the mask to be in that new layer on top of the image and then right click the layer and set it to be a mask.

I guess I can use Masks or separate it since I had some practice with it.