Timeline priorites?

[font=Lucida Console]hey guys… quick question

Im doing something similar to the vibration effect for a website and although the movie symbol used is on the lowest layer of my timeline, i can’t mask it or anything. its like its priority is above all other layers. what i mean is, for example, when i ctrl+enter to preview, the movie clip is showing on top of the other layers, when it should be masked. could anyone please help me with this?

thanks everyone! :)[/font]