Apple Under Scrutiny as Music Competition Rises  SAN FRANCISCO (Reuters) - Apple Computer Inc. &lt;A HREF="http://www.reuters.co.uk/financeQuoteLookup.jhtml?ticker=AAPL.O qtype=sym infotype=info qcat=news"&gt;AAPL.O&lt;/A&gt; may  have sold more than twice as many of its iPod digital music  players in its most recent quarter than its signature Mac  computers, but competitors are turning the up the heat in the  nascent online music industry.