i wanted to change my main menu icon (see below) from swirl to something else. alt-F2, then type gconf-editor. apps -> panel -> objects. i only had one object below that, but another site said you might have multiple. in mine, named object_2, check mark use_custom_icon and go up and select custom_icon and enter the path to the new image (see image). and it changes the icon to whatever you want. helped by http://forums.debian.net/viewtopic.php?t=14877