[Javascript] Named Layers in IE

[javascript@xxxxxxxxxx (Lau)]

I have a FORM that may have N fields with the same name.
How can I loop through them when I don't know how many there are... there may be none.

something like this:

for (i=1;i<N;i++){
  alert(document.Form1.MyField[i])
}

Thanks in advance
Lau