if (document.images) {
	myImages = [];  // [normal image, rollover image]
	myImages["about"] = ["graphics/about.gif", "graphics/about_on.gif"];
	myImages["books"] = ["graphics/books.gif", "graphics/books_on.gif"];
	myImages["home"] = ["graphics/home.gif", "graphics/home_on.gif"];
	myImages["links"] = ["graphics/links.gif", "graphics/links_on.gif"];
	myImages["order"] = ["graphics/order.gif", "graphics/order_on.gif"];
	for (i in myImages) {
		for (j in myImages[i]) {
			temp = myImages[i][j];
			myImages[i][j] = new Image();
			myImages[i][j].src = temp;
		}
	}
}

function show(tag,type) {
    if (document.images) {
        document[tag].src = myImages[tag][type].src;
    }
}