Texpaint works with three data types:

Skin textures
Model frames
S/T mappings


Skin textures can be either lbm or pcx files, and they will allways be
saved out the same size as loaded in, even if it is larger than the
active texture area.

Model frames are alias .tri files.  Adding support for 3ds would not
be difficult, but it is likely that there would be coordinate problems
unless the entire model was done completely in 3ds.

S/T mappings allow a skin to be mapped onto any model frame.  A mapping is
generated from a base frame and a texture size.  If a coords.txt file is
not present, texpaint will generate a default mapping that is compatable
with the output of the old texmake.  New skin or remap to skin will
generate a new coords.txt file.


Usage
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A three button mouse is required.

The left button paints with the current color in either the skin window
or the camera window, or selects colors in the palette view.  Ctrl-left
click picks up the color clicked on in any view, making it current.

Right button dragging slides the object or skin around.  Ctrl-right drag
to move in or out on the object.

Middle button dragging rotates the object in the camera view.  Ctrl-middle
drag to change the roll angle.