How can I make a negative of my layout prior to mask preparation?

Using the Boolean Tool dialog box, perform an INVERT operation on the layout. Then convert and send the inverted layout to the mask shop.
Note that as of dw-2000 v7.00, the Mebes, Cambridge, JEOL-01 and JEOL-51 output converters include an option to perform an INVERT operation prior to the conversion. This will save disk space since the inverted data is not created in the Library.