If you have DB Classic then you have a good converter already. It's called 3DS2X. You can call if from the CLI or search your hard drive for the location. It takes 2 parameters, the 3ds file name and the .x filename. Works even in cases where progs like Milkshape and Gamespace have trouble. I've heard it comes with Pro also but never have looked for it 'cause I already owned classic.
Quote: "DBP doesn't really support .3ds anymore"
Yes, DBP does support 3ds, but in between loading and actually using the model it converts the format internally. That happened in Classic also (the converter is named 3DS2X).