a = 6 
var pp = Math.random();
var foot = Math.round(pp * (a-1))+1;
function create() {
        this.src = ''
        this.border = ''
	this.alt = ''	
}
b = new Array()
for(var i=1; i<=a; i++) { b[i] = new create() }
b[1].src    = "images/main_01.jpg"
b[1].border = "0"
b[1].alt    = ""
b[2].src    = "images/main_02.jpg"
b[2].border = "0"
b[2].alt    = ""
b[3].src    = "images/main_03.jpg"
b[3].border = "0"
b[3].alt    = ""
b[4].src    = "images/main_04.jpg"
b[4].border = "0"
b[4].alt    = ""
b[5].src    = "images/main_05.jpg"
b[5].border = "0"
b[5].alt    = ""
b[6].src    = "images/main_06.jpg"
b[6].border = "0"
b[6].alt    = ""
var pic = "";
pic += '<img src='+b[foot].src+' border="0"'+' alt='+b[foot].alt+'>';
document.write(pic)