With Outlook closed, click Start>Run and enter %temp% (including the percent
signs) in the Open field.  Click OK.  Windows Explorer should open.  If the
Folders pane is not already showing on the left, click Folders on the
toolbar to show it.  Slide down past the Temp folder currently highlighted
and locate "Temporary Internet Files".  Click the plus sign to its left to
expand it.  Underneath you should see the OLKxxx folder.  Select it and
Explorer should show its contents.  Click Edit>Select All and then either
click Delete on the toolbar or click File>Delete or right-click the
selection and choose Delete.