Oprah Car Giveaway Generates Buzz for GM  DETROIT (Reuters) - Just ask "Anna Karenina" about Oprah.  The daytime talk show host, whose recommendation put the 19th  century novel on the best-sellers list, has generated a rush of  interest in General Motors Corp.'s &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GM.N target=/stocks/quickinfo/fullquote"&gt;GM.N&lt;/A&gt; new Pontiac G6  mid-sized car, GM officials said on Tuesday.