Rivals Say Microsoft Online Music Store Falls Short  SEATTLE (Reuters) - 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; newly  launched MSN Music download service has a long way to go to  catch up with iTunes and other online services, competitors  said on Thursday.