[Canaris]

Hm, i also didn't use the obj-format, but how the faces are written is very useful for work with SH3-geometry.
To add a material is very simple:

# Wavefront OBJ file
# header & blabla
mtllib NCL_Dido_boat02.mtl #use a file to specify the materials
g NCL_Dido_boat02 #objectname as group
v 0.000912 0.049299 -0.350204
v 0.000798 -0.063856 -0.287090
v -0.000745 -0.063856 0.282524
v -0.000864 0.049307 0.350204
# and so on
vt 0.860849 0.364295
vt 0.741674 0.314768
vt 0.980788 0.315139
vt 0.958285 0.357868
vt 0.965689 0.412230
# and so on
usemtl normal #specify the material by name(normal) that is used in following faces
f 2/3 3/2 7/1
f 7/1 15/4 2/3
f 8/6 15/4 9/5
f 9/5 1/7 8/6
f 15/4 8/6 2/3
# and so on
usemtl 2sided #specify the material by name(2sided) that is used in following faces
f 31/27 21/26 30/25
f 25/30 9/29 28/28
f 9/29 25/30 1/31
f 14/34 23/33 4/32
f 27/37 29/36 26/35
f 11/39 19/38 27/37
# and so on

and the materialfile NCL_Dido_boat02.mtl

# Wavefront material file
# header & blabla

newmtl normal    # specify a new material - named normal
         Ka 0 0 0                                         # ambient color - means what colors of ambient light are reflected (rgb)
         Kd  0.898039 0.898039 0.898039  # diffuse color - means what colors of diffuse light are reflected (rgb)
         Ks 1.000000 1.000000 1.000000  # specular color - - means what colors of specular light are reflected (rgb)
         illum 1.000000
         Ns 0.003922
         map_Kd NCL_Dido.tga  # specifys a mapfile for diffuse material
newmtl 2sided     # the same procedure as last year
         Ka 0 0 0
         Kd 0.898039 0.898039 0.898039
         Ks 1.000000 1.000000 1.000000
         illum 1.000000
         Ns 0.000000
         map_Kd NCL_Dido.tga

What Ns means i don't know. But i hope that helps a little bit.

MfG
Canaris

edit: i should learn to write faster