@perna: well no, it represents how tinted the specular color is by the diffuse. i interpolate between white and the diffuse color, based on this tint value. so mix(white, diffuse, tint).
You have your diffuse color set to black and your diffuse Texture is plugged in the reflective input. For metal materials you need a dark diffuse color but not for non metals.
Hoi! Does someone know if gameengines can (usually) handle materials where the alpha is, lets say, twice as big as the diffuse and normal map so: diffuse: 512^2 normal: 512^2 alpha: 1024^2 thx :)