Stocks Rise, Mergers, Retail Sales Help  NEW YORK (Reuters) - U.S. stocks added to earlier gains on  Monday after software maker PeopleSoft Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PSFT.O target=/stocks/quickinfo/fullquote"&gt;PSFT.O&lt;/A&gt; accepted  rival Oracle Corp.'s &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=ORCL.O target=/stocks/quickinfo/fullquote"&gt;ORCL.O&lt;/A&gt; \$10.3 billion sweetened buyout  offer and data showed better-than-expected November retail  sales.