function randomImage(numberOfOptions, imageDirectory, filePrefix)
{
   randNum = (Math.random()*numberOfOptions) + 1;
   randStr = String(randNum);
   dotIndex = randStr.indexOf(".");
   randIndex = randStr.substring(0,dotIndex);
   document.open();
   document.writeln("<a href='http://www.sas.com/corporate/advertising/'><img src='" + imageDirectory + "/" + filePrefix + randIndex + ".gif'></a>");
   document.close();
}