I don't know why you've buggered about removing all the dirt and grunge from your textures, you've seen our textures and we don't seem to have the trouble your having
lower the brightness in game to minimum as Mako suggested
Also YOU can save as 8bit 256 colours in CS3 so you should be able to save as it in CS4
1. First save your file as a PSD file
2. resize your image but make sure the resolution is set to 300 pixel/inch
3. go to image / mode / indexed color
5. click ok
6. you'll now see the indexed color window
7. set the palette to Local (doesn't matter which either perceptual, selective or adaptive) or possibly exact
8. if the color is not set to 256 set it as
9. set forced to none
10. options set both to none
11. click ok
12. save as BMP
13. another widow will come saying BMP Option set it as windows and 8 bit
Right you BMP still hasn't been saved correctly, now you will have to open it in another paint program
I've tried opening it in MSPaint and saving that was crap
I next tried Fireworks and saved it again that works if you set it as bmp 8 exact
I next tried PAINT SHOP PRO and that saved correctly also
I download Gimp
http://www.gimp.org/ and tried that but it wouldn't load so I could test it
So stop being a GIMP yourself and stop sodding about and get your hands on either Fireworks or Paint Shop Pro, you've managed to get your hands on Photoshop CS4 and I doubt very much that you paid for that not at $700 or even paid $1700 for the full Creative Suite.
Last thing please read the advise people are giving you, as the way I see it your skipping over it and making up as you go!
Now go back and read this again and one more time until you understand what we are trying to tell you!