myNum = 0;
myImage = new Array()
myImage[0] = "images/01.jpg";
myImage[1] = "images/02.jpg";
myImage[2] = "images/03.jpg";

function changeImg(){
spd = document.myForm.mySec.value*1000;
if(spd=="") spd = 8000;
document.myImage.src = myImage[myNum];
myNum++;
if(myNum >= myImage.length) { myNum = 0 }
myTimer = setTimeout("changeImg()",spd)
}