Where is that Desktop Policy Settings tab hiding?
In Domino Administrator, if you're ever looking for the Diagnostics, Custom Settings, or Administration tabs in the Desktop Policy Settings document, remember to click the scroll buttons at the far right of the document header:
Clicking them three times reveals all the additional tabs.
The same advice applies for any other document in the Domino Directory. If you've been directed to a tab and can't see it, look for buttons like the ones above.