Now I can't remember how I did it before, but I tried renaming the rom to 'blabla.nds, but it still says 'file type: .nd5' So now it comes out as blabla.nds.nd5. Enlighten me please.
Open My Computer or any folder. Windows Vista/7 press Alt to bring up the Menu Bar.
Tools -> Folder Options -> View -> Untick 'Hide extensions for known file types'.