Also for Asp.net you can use this JavaScript in your HTML source.
<script language="JavaScript">
function onkey()
{
if (window.event.keyCode==13)
{
Form1.BUTTON_ID_HERE.focus();
}
}
</script>
Hope these help
Also do not for get to add the onKey() function to your body onkeydown event.
<body onkeydown="onkey();" ...