var wall = new Array();

/* 使用する背景画像を好きなだけ記述 */
wall[0] = "http://suyamanatsuki.polka3.com/img/decoration/d.gif";
wall[1] = "http://suyamanatsuki.polka3.com/img/decoration/d.gif";
wall[2] = "http://suyamanatsuki.polka3.com/img/decoration/d.gif";
wall[3] = "http://suyamanatsuki.polka3.com/img/decoration/d2.gif";
wall[4] = "http://suyamanatsuki.polka3.com/img/decoration/d3.gif";

var rnd = Math.floor((Math.random() * 100)) % wall.length;
document.write('<style type="text/css">#decoration { background-image:url(' , wall[rnd] , ') ; }</style>');