No free 3D programs make DBO files
.DDS is an image file type
.MTL is the material file for .OBJ
So .mtl will export with .obj if you have a material to go along with the model.
You can use a program called GIMP
to export .dds with a free dds exporter plugin.
If you want a free DBO exporter, you could just write an .x to .dbo converter in DBP. It's pretty darn simple.
If you want a program that exports and imports to the .obj format then Blender 3D
will do that for you and it's 100% completely free. No strings attached.