var mess = new Array(
'<img src="images/homepageimage1.jpg" width="745" height="176" alt="" border="0">',
'<img src="images/homepageimage2.jpg" width="745" height="176" alt="" border="0">',
'<img src="images/homepageimage3.jpg" width="745" height="176" alt="" border="0">');
var max = mess.length;
var num = Math.floor((Math.random() * max));
document.writeln(mess[num]);