var offImageCache = new Array();
var onImageCache = new Array();

var npics = 7;
for( var i = 0; i < npics ; i++ ) {
   offImageCache[ i ] = new Image( 106, 40 );
   onImageCache[ i ]  = new Image( 106, 40 );
}

offImageCache[0].src = "images/home.jpg";
onImageCache[0].src  = "images/home-on.jpg";
offImageCache[1].src = "images/about.jpg";
onImageCache[1].src  = "images/about-on.jpg";
offImageCache[2].src = "images/officers.jpg";
onImageCache[2].src  = "images/officers-on.jpg";
offImageCache[3].src = "images/constitution.jpg";
onImageCache[3].src  = "images/constitution-on.jpg";
offImageCache[4].src = "images/discussion.jpg";
onImageCache[4].src  = "images/discussion-on.jpg";
offImageCache[5].src = "images/schedule.jpg";
onImageCache[5].src  = "images/schedule-on.jpg";
offImageCache[6].src = "images/directions.jpg";
onImageCache[6].src  = "images/directions-on.jpg";

function imageOn( img, i ) {
   img.src = onImageCache[i].src;
}

function imageOff( img, i ) {
   img.src = offImageCache[i].src;
}