I've looked for tutorials, but so far I have had no luck.
How do I create a multipurpose bitmap?

So does anybody have a tutorial I can follow?

Use this to post a reply.
http://forum.halomaps.org/index.cfm%3Fpage=newreply&topicID=32031#NEWMSG

A multipurpose map comprises of 4 seperate bitmaps added into 1 bitmap using the RGBA channels.

R/Red channel is where you put in the specular mask. This mask regulates the amount of reflectivity, and how much the cubemap shows up on each part of the bitmap. White is full reflectivity, black is none. And the grays are inbetween.

G/Green channel is where you put in the self illumination mask. It is used to give a certain part of the bitmap a self glow. Such as if its in the shadows, it would be lighted up. Make parts white if you want it to glow, and black if you don't want it to glow.

B/Blue channel is where you put in the detail mask. Regulates the visibility of the detail map that is added into the shader.

A/Alpha channel is where you put in the change color mask. This is what allows a certain part of the bitmap to change colors, due to multiplayer purposes, or for permutations. An example of this is the cyborg biped, the armor is white. Where the armor is white, is also where the mask would be white, with the parts that don't change color being black.