DoubleClick Signs on MSN to Use Its Rich Media Ads  NEW YORK (Reuters) - A top executive for Web marketing  company DoubleClick &lt;A HREF="http://www.reuters.co.uk/financeQuoteLookup.jhtml?ticker=DCLK.O qtype=sym infotype=info qcat=news"&gt;DCLK.O&lt;/A&gt; on Tuesday said Microsoft Corp's  &lt;A HREF="http://www.reuters.co.uk/financeQuoteLookup.jhtml?ticker=MSFT.O qtype=sym infotype=info qcat=news"&gt;MSFT.O&lt;/A&gt; MSN Web portal will use its rich media ads online,  paving the way for wider use of a key DoubleClick  product.