Stocks Set to Open Flat to Lower Today  NEW YORK (Reuters) - Stocks were set to open flat or  slightly lower on Monday as Microsoft Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MSFT.O target=/stocks/quickinfo/fullquote"&gt;MSFT.O&lt;/A&gt; begins to  trade ex-dividend, weakening technology shares and offsetting a  welcome drop in crude prices.