today=new Date();
jran=today.getTime();
function rnd() {
ia=9301;
ic=49297;
im=233280;
jran = (jran*ia+ic) % im;
return jran/(im*1.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
document.write("<center>");
for(i=1;i<=1;i++) {
myNum=(rand(4)); //改成你要随机显示的图片数；
if(myNum == 1) document.write("<img src='images/sub_banner1.jpg' border=0>"); //图片路径，可用http://
if(myNum == 2) document.write("<img src='images/sub_banner2.jpg' border=0>"); 
if(myNum == 3) document.write("<img src='images/sub_banner3.jpg' border=0>"); 
if(myNum == 4) document.write("<img src='images/sub_banner4.jpg' border=0>"); 
else {
document.write();
}
};
document.write("</center>");