For bitmaps, use multi-texturing. Each texture unit respectivly would be your base(colored) texture and your alpha-map. From there, use OGL blending functions.
Code:
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glActiveTextureARB(GL_TEXTURE0_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, g_Texture[textureID]);
glActiveTextureARB(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, g_Texture[textureID]);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 1.0);glVertex3f(0.5, 0.5, 0.0);
glTexCoord2f(0.0, 0.0f);glVertex3f(-0.5, 0.5, 0.0);
glTexCoord2f(1.0, 0.0f);glVertex3f(-0.5,- 0.5, 0.0);
glTexCoord2f(1.0, 1.0);glVertex3f(0.5, -0.5, 0.0);
glEnd();
I'm 80% sure this would, work, but i'm no guru nor do I have self-confidence, lol
-psychopath