<script language="javascript" type="text/javascript">
function stopRKey(evt) {
	var evt  = (evt) ? evt : ((event) ? event : null);
	var node = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);
	if ((evt.keyCode == 13) && (node.type=="text")) { return false; }
}
document.onkeypress = stopRKey;
</script>

http://www.mediacollege.com/internet/javascript/form/disable-return.html

Prevents the return key from submitting the form.

forms

JavaScript