if (screen.height >= 768 && screen.width >= 1024) {

document.write("<img src='http://www.thriller.tk/pic/topbig.jpg' width=1003 height=70 border=0>");

}

else {

if (screen.height <= 600 && screen.width <= 800) {

document.write("<img src='http://www.thriller.tk/pic/topsmall.jpg' width=779 height=70 border=0>");

 }

}