You need alpha mask for the glow. Take the current phongmask from the alpha channel of the diffuse (if you have one), create a normal map (can be flat too, doesn't really matter) and place the phongmask on the alpha channel of the normal map.

Next, you paint the alpha channel of the diffuse texture black, and the parts you want to glow white (its linear though, white=100% glow, 50% gray = 50% glow ect. so if you want some places to glow more then others, use different shades)

Then you do the vmt as follows:

*Any other vmt parameter you need*

Ask away if something is unclear.

Well in layman's terms:

lets pretend you're editing the shotgun.

============= - Open v_shotgun in photoshop, gimp, or whatever .vtf/.tga capable image editing software you've got.

- Add the textures you want to glow, then tab over to the color channels and add an alpha map, where everything except what you want to glow is masked out in black.

- Save this as your new texture, then create a new blank normal map and save it as vshotgunnormal or whatever.

- In your vshotgun.vmt, it would read similar to the code posted above, substituting the directory of your vshotgun.vtf and vshotgunnormal.vtf in the appropriate places.

Basically, the code is telling the shading on the model to act independent of outside light sources, so even in the dark, parts of the model still "glow." If you don't mask out only the parts you want glowing, the entire model stays illuminated, even in pitch black, which looks really horrible.