3Com to Buy TippingPoint for \$430 Mln  CHICAGO (Reuters) - 3Com Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=COMS.O target=/stocks/quickinfo/fullquote"&gt;COMS.O&lt;/A&gt; on Monday said it  will buy network security firm TippingPoint Technologies Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=TPTI.O target=/stocks/quickinfo/fullquote"&gt;TPTI.O&lt;/A&gt; for about \$430 million, as 3Com expands its  telecommunications equipment offerings to compete better in the  market for large corporate users.