How to find unique element.

Hi,
I am learning xsl and have got a problem

we have a xml which looks like:
<?xsl version="1.0"?>
<company>
      <Employee empcode="1">
             <project pcode="p1">
	      <duration hours="10" />	 
	</project>
	<project pcode="p2">
	       <duration hours="8" />	 
	</project>
      </Employee	>
      <Employee empcode="2">
             <project pcode="p1">
	      <duration hours="14"/>	 
	</project>
	<project pcode="p2">
	       <duration hours="6" />	 
	</project>
            <project pcode="p3">
	       <duration hours="12" />	 
	</project>
      </Employee	>
</company>   
Problems:
1) How do i find out unique projectcodes?
2) How to display the total hours put in by all the employees in a
particular project?

Any information regarding sites related to xsl will definitely help me 
Thanks.


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