image change fails

I have a function called onload that includes this:


window.onload=new function(){

...

if (menuletter!=false){
document.cookie="hddrv="+(menuletter)+"; path=/; expires="+exp.toGMTString();
document.enterIndex.src='enter2.gif';
// window.setTimeout("goIndex()",7000);
// return false;
}
...

}

<img border="0" name="enterIndex" src="enter1.gif" width="413" height="41">


If I uncomment the two lines and comment the document image swap line, they execute perfectly, so the routine works.

But if I try to do the image swap instead of the two commented lines, it doesn't swap.

Of course, the image enter1.gif and enter2.gif exist.

What am I doing wrong?

1. remove the "new" keyword from the onload function
2. what is menuletter?
3. what is goIndex() ?