Right, let's see if I can explain this in an understandable fasion.
What Coda means by needing seperate textures is this:
Glow, bump, and envmapping can be applied to textures as a whole, but not parts of textures. If you apply (for example) an envmap to the vanguard unit, the envmap will apply to the
whole texture. If you only want his helmet to be envmapped, you need to re-UV the model to use one texture for the body and another, seperate texture for the helmet (or whatever part you want to envmap).
UV is the way that a model's texture is applied to the model.
This:
CodaRez wrote:UV-ed basic translation: re-textured.
is slightly misleading. The basic translation of re-UVed is "remapped the texture", which involves a modelling program (usually XSI).
For what you want to do, you'd need to use Meshtool to turn the vanguard's msh into a .obj file. This you'd need to import into XSI and texture, then you'd need to disconnect the helmet polys and give them a renamed copy of the texture the rest of the model uses. Then you'd need to envelope the model and export it.
This is a in-depth procedure that will probably be challenging for someone new to modding (as I assume you are), and since you'll need guidance along the way, I'd recommend making another help topic in the 3D Modelling forum, where you can get more answers specific to this process.