Hopefully you’ll be able to answer a question for someone still stuck using SP2007!
I have DFFS front end and back end files both loaded and working correctly. For the vlookup plugin I have the 2007 frontend (v.2.114) combined with the SP2010/13 backend file (v2.203)
When I make the vLookup field visible on a tab in the disp/edit forms, it does not show any lookup data or column names. In the dispform the field shows blank and in the editform it shows as an editable single line text field. Strangely though, when I edit the page of either form, the default form webpart shows the vlookup field with all the columns, add/edit buttons that I made in the vlookup setup. When I come out of edit mode and the DFFS settings are applied, the vlookup doesn’t work.