Diffuse maps

[etx527]

i have been making some things in Maya 2011 i export it as a obj and open it in .nif scope and save it as a .nif file, but when i try to open it in the GECK it tells me that it is missing a diffuse map. so my question is how would i go about creating one so i can use it in fallout 3?

also screen shots would be helpful.