Thats pretty simple. Start with the code i gave you bfore (or your own that does the same) Simply create a header div that will contain your heading and give it a background image with the same techniques as used on the body but make the image a .PNG which is a gradient from nothing to a darker colour.

Because PNGs allow alpha channel (trasparencies) when it is overlaid in your body background-image it will look as if it darkens towards the top.

Does this make sense?