var imagenumber = 21 ;
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;
images = new Array
    images[0]='http://www.AtRiskEducation.Net/images/product_thumb01.jpg'; 
    images[1]='http://www.AtRiskEducation.Net/images/product_thumb02.jpg'; 
    images[2]='http://www.AtRiskEducation.Net/images/product_thumb03.jpg'; 
    images[3]='http://www.AtRiskEducation.Net/images/product_thumb04.jpg'; 
    images[4]='http://www.AtRiskEducation.Net/images/product_thumb05.jpg'; 
    images[5]='http://www.AtRiskEducation.Net/images/product_thumb06.jpg'; 
    images[6]='http://www.AtRiskEducation.Net/images/product_thumb07.jpg'; 
    images[7]='http://www.AtRiskEducation.Net/images/product_thumb08.jpg'; 
    images[8]='http://www.AtRiskEducation.Net/images/product_thumb09.jpg'; 
    images[9]='http://www.AtRiskEducation.Net/images/product_thumb10.jpg'; 
    images[10]='http://www.AtRiskEducation.Net/images/product_thumb11.jpg'; 
    images[11]='http://www.AtRiskEducation.Net/images/product_thumb12.jpg'; 
    images[12]='http://www.AtRiskEducation.Net/images/product_thumb13.jpg'; 
    images[13]='http://www.AtRiskEducation.Net/images/product_thumb14.jpg'; 
    images[14]='http://www.AtRiskEducation.Net/images/product_thumb15.jpg'; 
    images[15]='http://www.AtRiskEducation.Net/images/product_thumb16.jpg'; 
    images[16]='http://www.AtRiskEducation.Net/images/product_thumb17.jpg'; 
    images[17]='http://www.AtRiskEducation.Net/images/product_thumb18.jpg'; 
    images[18]='http://www.AtRiskEducation.Net/images/product_thumb19.jpg'; 
    images[19]='http://www.AtRiskEducation.Net/images/product_thumb20.jpg'; 
    images[20]='http://www.AtRiskEducation.Net/images/product_thumb21.jpg'; 
var image = images[rand1]