Just at the end of last month, when I wanted to modify the Mr whoopee textures for Grand Theft Auto 3, I simply imported the .dff and it worked fine, same for Vice city's Ice cream van. In the end all I needed to do was just edit the TXD files.
Sort of silly to go all around the houses of trying to change the appearance via Zanoza modeler.
I just went into the GTA3 img file for vice city and extracted the Python, quite a nice gun in that game. And I loaded Zanoza modeler, imports fine.http://img809.imageshack.us/img809/9868/pythonweapon.jpg
Have you considered trying to install Zanoza modeler again? How long has it been installed for? Mine has been since I did my last windows xp home edition restart almost two years ago.