Ok i figured this out today (im using photoshop 7.0 so if you dont have it this will be a little harder) first what you do is you make ur texture in a normal RGB setting, then you copy and paste that texture in a new window with a gray scale setting so the texture is gray, then u copy and paste the original texture in a bitmap which should have a lil bit of coulour or noise change. Then you have 3 different couloured textures like the picture below
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After you have that u copy the bitmap image and paste it in the original RGB images box and set the transparency to about 5-10% then you take the grayscale and copy and paste it into the RGB texture box and set the transparentcy from 50-80% ill let you judge on what percent looks best! then copy the grayscale again and paste it in the original RGB box and make sure its a lil off so its like a shadow then make its transparentcy/opacity to what you think is best!
I did this whole thing with my box texture and the results were excellent!
Heres the result!
The qualitys a lil crappy cuz i saved the image in low quality so it wouldent be hard to view for you dial up ppl!
If the image doesent show up copy and paste this address into your address bar: http://www.freewebs.com/phoenixfx/AFTER.jpg