Wal-Mart's Sept. Sales Up 2.3 Percent  CHICAGO (Reuters) - Wal-Mart Stores Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=WMT.N target=/stocks/quickinfo/fullquote"&gt;WMT.N&lt;/A&gt; on  Saturday said sales at stores open at least a year rose 2.3  percent for September, near the low end of expectations,  according to its preliminary tally.