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(3)); //改成你要随机显示的图片数；  
if(myNum == 1) document.write("<img src=images/nail7.gif>"); //图片路径，可用http://  
if(myNum == 2) document.write("<img src=images/nail8.gif>");   
if(myNum == 3) document.write("<img src=images/nail9.gif>");  
else {  
document.write();  
}  
};  
document.write("</center>");