When you add an importer, you pass the funtion that AC3D will call to load an object e.g.
Code:
ac_register_file_importer("3DS", ".3ds", "3D Studio", ac_import_3ds, ac_import_3ds_info);
ACObject *ac_import_3ds (char *filename)
{
// open the file
// create AC3D object structures
// return the top object
}
the sv import code from the SDK is a simple example of how to create an object structure.
Andy