Hi Fencer,
Are you using Bright? I had to stop using it to export my bmps, because it uses 8-bit depth, and the Normal and Diffuse maps need to be 32-bit depth now. I think that probably explains the difference between a 1 MB vs 4 GB file size - the color bit depth is 8 rather than 32 bits.
The other files - Specular, Power, and Environment, should be saved as 8-bit grayscale images.