Dow Near Flat; Nasdaq, S P 500 Down  NEW YORK (Reuters) - U.S. blue-chip stocks rose slightly on  Thursday after a court gave a boost to Altria Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MO.N target=/stocks/quickinfo/fullquote"&gt;MO.N&lt;/A&gt;  and other tobacco companies, but that was offset by a drop in  McDonald's Corp. on new mad-cow worries.