Maybe you didn't include the media query the right way, here is an example of your CSS along with a media query which makes the background go when the browser window is 600px width or less.
body {
background-repeat: no-repeat ;
background-image: url("http://dl.dropbox.com/u/19831829/Sour%20Milk%20Website/sidework copyR.png"), url("http://dl.dropbox.com/u/19831829/Sour%20Milk%20Website/sideworkL.png");
background-attachment: fixed;
background-position: left, right
}
/**
* Remove background if window width is 6OOpx or less
*/
@media all and ( max-width: 600px ) {
body {
background: none;
}
}
Working example: http://codepen.io/anon/pen/sfLmo (resize your browser to test)
Cheers.