ASP.Net page enter key causing post back

<script language="JavaScript">
var nav = window.Event ? true : false;
if (nav) {
window.captureEvents(Event.KEYDOWN);
window.onkeydown = NetscapeEventHandler_KeyDown;
} else {
document.onkeydown = MicrosoftEventHandler_KeyDown;
}

function NetscapeEventHandler_KeyDown(e) {
if (e.which == 13 && e.target.type != 'textarea' && e.target.type != 'submit') { 
return false; 
}
return true;
}

function MicrosoftEventHandler_KeyDown() {
if (event.keyCode == 13 && event.srcElement.type != 'textarea' && 
event.srcElement.type!= 'submit')
return false;
return true;
}
</script>

source : http://stackoverflow.com/questions/4209903/asp-net-page-enter-key-causing-post-back