¿Lo estás asignando entre comillas?
<script language="JavaScript">
<!--
var y = "mi casa";
var x = y + ";";
alert(x);
//-->
</script>
<hr noshade size=1 color="#000000"><img src="http://www.gograph.com/Images-8712/ClipArt/cat03.gif" height="50" border=0 align="absmiddle"> <font size="2" face="verdana" color="#000000">
bet[/CODE]