site navigation

hello,
I want that when i scroll only the main content (the projects area) will be affected.
how can i do this?
actually, i think what i'm looking for is some kind of a mask - that will hide the project text when the user is scrolling down.
(now when i scroll down - the project text move up - below the tag menu - that is what i am trying to prevent...)
another thing - now when i scroll down - the site logo is scrolling as well. how can i prevent it from moving?

thank you...