Document Search - ship to address search help

All,

We are extended classic scenario (7.01 SP 10).

When we go to Document Search - for Purchase Orders and we pick Ship To Address - it provides us with a list of all the ship to addresses - instead of allowing us to enter some selection criteria.    When I click on Product Category it allows us to enter search criteria as you can see from the print screen below.   For Ship To Address - it provides the list of all plants instead of a pop-up box to narrow down the search.   How do we get a search help for the Ship To Address?

Thanks

Sandra