Microsoft Excel 2003 
  1. Select all the rows, including the column headers, in the list you want to filter.
  2. On the Data menu, point to Filter, and then click Advanced Filter. 
  3. In the Advanced Filter dialog box, click Filter the list, in place. 
  4. Select the Unique records only check box, and then click OK. The filtered list is displayed and the duplicate rows are hidden.
  5. On the Edit menu, click Office Clipboard. The Clipboard task pane is displayed.
  6. Make sure the filtered list is still selected, and then click Copy. The filtered list is highlighted with bounding outlines and the selection appears as an item at the top of the Clipboard.
  7. On the Data menu, point to Filter, and then click Show All. The original list is re-displayed.
  8. Press the Delete key. The original list is deleted. 
  9. In the Clipboard, click on the filtered list item. The filtered list appears in the same location as the original list.
Microsoft Excel 2007
Refer to instructions in Microsoft's Knowledgebase to filter for unique values or remove duplicate values:

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