change background image

Trying to change my background image from standard color to a wood grain effect in template/image/tile_back.gif. Is this the correct file to replace? When I replace the file in default it saves but when I replace the file in classic it reverts back to the original zen gif even after I delete it and my index page still show classic color. I'm using 1.5.0

Depends on what you mean by 'background image'. A link to the site would help. If you mean the area behind the mainWrapper, you would specify a background-image in the 'body' rule in the stylesheet.