//store the pics in arrays
pics = new Array(11);
pics[0] = "picture_01.gif";
pics[1] = "picture_02.gif";
pics[2] = "picture_03.gif";
pics[3] = "picture_04.gif";
pics[4] = "picture_05.gif";
pics[5] = "picture_06.gif";
pics[6] = "picture_07.gif";
pics[7] = "picture_08.gif";
pics[8] = "picture_09.gif";
pics[9] = "picture_10.gif";
pics[10] = "picture_11.gif";

//calculate a random index
index = Math.floor(Math.random() * pics.length);
//display picturechoice
document.write("<img src=\"images/hp/" + pics[index] + "\" height='250' width='350' border='0'>");