"Enter Key" Behaviour to "Tab Key"

[LJS1]

Hi all,
I want to change the behaviour of "Enter Key" to Tab key" on the TextBox.
In the TextBox ie Txt1 , Autopostback is true and onkeypress event I am calling the Client side Javascript
<script language=javascript>
function TranslateKey(){
if (window.event.keycode == 13) {
window.event.keycode ==9;}
}
</script>
But it is not working. Any Idea....?
Thanks
LJS