well, i managed to get one applied to a 3ds file converted, what you need to do, is make a folder (youraddon/textures) and put the textures there, then, in the program you made the model (3d max, maya etc), texture it there.
Extract it as a .3ds when done and tick a box if it asks to preserve the texture coordinates.
Import it into O2 and save the .p3d into the youraddon folder, open the texture window at the side, and double click (while hold ctrl) the texture to highlight the faces used by that texture, hold ctrl and click in the front window, and press E.
A new window will open, and at the bottom, there should be a text box to point to the new texture files, browse to the texture in youraddon/texture and click apply, this "should" make it appear in the o2 viewer.
Do the same for the rest of the textures and your all set.
Hope that helps (if i got something wrong then please pm me and i'll try and rectify it)