CSS: background-attachment

Specifies whether or not the background image is fixed or scrollable as a user scrolls the document.

Browser/User Agent Support

IE	Netscape	Mozilla	Opera	Safari
5.0+	6.0+	1.0+	4.0+	1.0+
IE: IE uses the value "local" instead of "scroll".

["scroll" | "fixed"]

inherit	Inherit the value from the parent element.
scroll	Background image scrolls with the document.
fixed	Background image is fixed as the document scrolls.

For additional information and a demonstration of the background-attachment attribute, see the demo page on quirksmode:

W3C�CSS2