the enviromap.tga...
an easy way is to take a screenshot (F6) during gameplay(1st person view, no gun),its called "Shot_0" or something in your work folder...
Make the screenshot 256x256, make it tileable.
this way it seems like its reflecting your environment.

If you want selective reflections on your model, add a alphachannel in photoshop to your model's texture.
its greyscale, so white would be completely reflective (showing enviromap) grey would be sort of reflective, and black none.
Save it as 32bit .TGA and apply it to your model as skin1.
Hope that helps