Using only SPD on a MOSS site, is it possible to customize the default form
shown when users do a single or multiple file upload into a DocLib?

The problem we are trying to solve is that we have a required field in DocLib
which is a lookup into a custom list, but here could be hundreds of items in the
list. Thus, we would like to filter or cascade the drop-down on the upload form
which populates this required field in the DocLib.