Selecting all ancestors

Hi:
Based on the following tree, I want to select all the
parents for an specific catid. I.e for catid="3" I
should select id's 1 and 2. This tree coul have
different levels. 

<root>
  <cat catid="1">
    <cat catid="2">
       <cat catid="3"/>
    </cat>
  </cat>
</root>       

Thanks.

__________________________________________________
Do you Yahoo!?
Faith Hill - Exclusive Performances, Videos & More
http://faith.yahoo.com

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list